(covers information from several alternate timelines)
Alexander Rozhenko, also known as Alexander, son of Worf, was the son of Starfleet Lieutenant Worf and Federation Ambassador K'Ehleyr; thus he was three-quarters Klingon. He was a member of the House of Mogh and the House of Martok. (TNG: "Reunion", "New Ground")
Alexander was conceived during a brief encounter between Worf and K'Ehleyr when, in 2365, the ambassador came aboard the USS Enterprise-D in an effort to defuse a potential crisis presented by the return of a Klingon K't'inga-class battle cruiser, the IKS T'Ong, that had been dispatched decades before as a sleeper ship. (TNG: "The Emissary", "Reunion") After the crisis was successfully resolved, K'Ehleyr departed the Enterprise. (TNG: "The Emissary") She concealed her pregnancy and the birth of Alexander from Worf. (TNG: "Reunion") Alexander was born on the forty-third day of Maktag, stardate 43205. (TNG: "New Ground") Worf later stated to Miles O'Brien that he never saw his son when he was a toddler, and that it was "something I will always regret." (DS9: "Business as Usual")
Alexander's conception and birth were finally revealed to Worf by K'Ehleyr approximately one year later, when she returned to the Enterprise as part of a contingent representing K'mpec in his efforts to persuade Jean-Luc Picard to act as the Arbiter of Succession for the Klingon Empire. Until that point, Alexander had lived with his mother, not knowing who his father was.
Despite a coy attitude meant to antagonize Worf, K'Ehleyr wanted Worf to acknowledge Alexander as his son. Worf was reluctant to do so because of his recent discommendation and the dishonor that Alexander would be forced to share as a result. However, despite his concerns, Worf was forced to acknowledge the relationship of K'Ehleyr and Alexander to him when K'Ehleyr was killed by Duras because she had been investigating the circumstances surrounding the Khitomer Massacre and Worf's discommendation.
Although Worf took custody of Alexander following K'Ehleyr's death, he was sent to live on Earth with Sergey and Helena Rozhenko, Worf's adoptive parents, who were identified as his grandparents. (TNG: "Reunion")
Aboard the Enterprise-D
Alexander was brought back onboard the Enterprise-D one year later by Helena Rozhenko. During his time on Earth, Alexander had had problems adjusting. Though smart and high-spirited, he was not always truthful and was sometimes difficult to control. Helena and Sergey believed that Alexander's behavior problems were not unusual for a boy of his age, but could only be solved by the presence of his father. Helena also admitted that the two of them were too old and ill-equipped to raise a Klingon child, even one who was ¼ Human. (TNG: "New Ground")
Alexander wasn't a "typical" Klingon child, considering that he had lived with Humans for most of his life. Initially, the adjustment to living on the Enterprise was very difficult. Much to his father's dismay, Alexander displayed tendencies toward telling lies and even was guilty of small instances of theft. Even after his father disciplined him, Alexander's behavior was a problem in school, causing Ms. Kyle to report to Worf that his defiance, along with continued theft and lying, was disrupting the class. His disobedience to Worf and disregard for the instructions of his elders and ship's regulations eventually came to a head when Alexander was nearly killed in a fire in the ship's biolab. (TNG: "New Ground")
Alexander eventually settled into life on the ship and made friends, but the adjustment took time. Deanna Troi took a special interest in the child and his difficulties adjusting to the ship and his father. The two developed a strong relationship, so much so that Worf asked the counselor to be Alexander's guardian when it appeared he might die following a dangerous medical operation. (TNG: "Ethics") Alexander was also friendly with Counselor Troi's mother, Lwaxana Troi, who came aboard the Enterprise in 2368 to be wed to Campio. In their brief time together, Alexander and Lwaxana spent time together on the holodeck and became good friends, much to his father's dismay. (TNG: "Cost of Living")
While onboard the Enterprise, Alexander at one point developed a Deadwood holodeck program with the help of Reginald Barclay in 2369. Despite his efforts to find extra duties for himself, Worf agreed to participate in the program as a means of interacting with his son and improving their relationship. To his surprise, Worf enjoyed the program, especially his role as the sheriff with Alexander as his deputy. Initially, the program was too easy and Alexander was disappointed, so he ordered the difficulty level be reset to four, forcing his father to expend more effort in apprehending the criminal characters. At the same time, Lieutenant Commanders Geordi La Forge and Data were conducting an experiment which went awry and influenced the program. The main characters took on the appearance and abilities of Data, and the holodeck safeguards were removed, making the 19th century firearms lethal and placing Alexander in jeopardy. Alexander eventually escaped, but he worried that the episode would mean his father would never again visit the program. His father assured him that, if the town of Deadwood were to be threatened again, they would need a sheriff… and a deputy. (TNG: "A Fistful of Datas")
In 2369, Alexander helped Captain Picard and others regain control of the ship from DaiMon Lurin. The captain, along with Ro Laren, Keiko O'Brien, and Guinan, had passed through a molecular reversion field that had reverted them to a stage of physical youth. Blending in with the ship's civilian children, they re-took the ship. Alexander participated in their plan by distracting several of their guards and stealing items from sickbay. (TNG: "Rascals")
In 2370, an adult Alexander, who had traveled back in time from forty years in the future, made contact with Worf and Alexander, posing as K'mtar, gin'tak to the House of Mogh. In an attempt to change history, he tried to convince Worf that his young counterpart needed to be trained in the ways of a Klingon warrior. When it became apparent that his counterpart was not willing to do so, however, he attempted to kill him, only to be stopped by Worf. He explained to Worf that, in his time, Worf had been assassinated on the floor of the High Council, due to Alexander's attempts at bringing peace to the Empire. Wishing to prevent this future, he had traveled back in time in an attempt to ensure that his counterpart would not grow up to be a diplomat, but rather a warrior who could fight at his father's side. Worf told him that, now that he had disrupted the flow of history, his death was no longer a certainty, and that he would be proud of his son no matter what path he chose to follow. After hearing these words, the adult Alexander departed, but not before expressing his love for his father. (TNG: "Firstborn")
Following the destruction of the Enterprise-D in 2371, Worf sent Alexander back to Earth to live with his foster parents while he journeyed to Boreth during an extended leave from Starfleet. Upon returning to active service, he chose to leave Alexander on Earth, believing he was far happier there than he was living with him. (DS9: "The Way of the Warrior")
Service to the Empire
In 2374, after years of avoiding Klingon culture, Alexander enlisted in the Klingon Defense Forces at the height of the Dominion War. He was given the rank of bekk and assigned to the IKS Rotarran under General Martok and Worf, where he manned the ship's sensor console. He had severe trouble serving with other Klingons, as he was unskilled as a warrior and displayed many Human traits that the other crew members found soft and disgusting.
Alexander's adjustment to life among Klingons was difficult. He was unable to offer a full explanation for his change of heart to either Worf or Martok but seemed to recognize, as he reached Klingon maturity, that his path lay with his people. Though none questioned his commitment, his combat skills were sorely lacking, and his lack of knowledge of Klingon customs hurt his standing on board. Upon being reunited, Alexander was emotionally cold towards Worf and was resentful and bitter at being abandoned by his father. Alexander also corrected Worf in conversation when Worf referred to his adoptive parents as Alexander's grandparents. (DS9: "Sons and Daughters")
Moreover, his presence on the vessel proved a trial for Worf and a source of resentment among the crew. At Martok's urging, Worf attempted to mend his relationship with Alexander, both as a father and a first officer. Martok advised Worf to let matters essentially tend to themselves; that Alexander would find a place on the ship, and by extension, learn about Klingon culture along the way. Though he might suffer some broken bones, as well as other injuries, he would survive. When Alexander forgot to clear a battle simulation from the sensors, he called an alert, believing they were under attack. When the mistake was realized, the crew laughed. Martok told Worf the crew had accepted Alexander, and Worf replied yes, as the ship's fool.
Tension continued between Alexander and Worf when Martok agreed to Worf's request to have Alexander transferred off the ship at the next opportunity, due to Alexander's inability to master basic combat skills and his ongoing resentfulness towards Worf, which clouded his judgment as well as his lack of a real answer when Martok challenged his motivations. All of these made Martok believe Alexander unfit for battle. Alexander accused Worf of never accepting him. The Rotarran was attacked shortly after. While attempting to make repairs, Alexander managed to lock himself into a corridor, the ship's fool once again. When Worf observed the affection the crew held for Alexander and his own graceful acceptance of the role, Worf changed his mind about transferring Alexander off the ship, telling Alexander, "I cannot fix the mistakes I have made, but from now on I will stand with you. I will teach you what you need to know to be a warrior, and you will teach me what I need to know to be a father." Alexander challenged Worf by saying, "Let's see if you mean it." Eventually, the two reached a full reconciliation that led to Alexander joining the House of Martok. (DS9: "Sons and Daughters")
Alexander continued his service aboard the Rotarran and strengthened his relationships with his fellow Klingons. He continued to make mistakes, such as flooding an entire corridor with superheated hydraulic fluid. This did not strain his position within the ship, however, as the crew considered him a good luck charm; the more mistakes Alexander made, the fewer they would make in battle. Later that year, along with most of the Rotarran's crew, he transferred to the IKS Ya'Vang, where he hoped the goodwill toward him would continue. (DS9: "You Are Cordially Invited")
Worf considered Alexander to be more Human (in personality and interests) than Klingon and tried desperately to change him. (TNG: "Reunion", "New Ground", "Cost of Living") It wasn't until the revelation that K'mtar was actually an older Alexander from an alternate future that Worf began to accept his son for who he was. (TNG: "Firstborn")
Alexander only knew his mother briefly, but his love for her, and hers for him, remained with him his entire life. Likewise, her death marked him forever. It was the first time Alexander had seen death, and the powerful image of Worf over the bloody body of K'Ehleyr was particularly difficult for him. (TNG: "Reunion")
Many years later, the fear of losing his father in the same way that he had lost his mother haunted Alexander and drove him to travel back in time in order to prevent his father's death. (TNG: "Firstborn")
From the beginning, Worf had a hard time adjusting to the presence of Alexander in his life. He was particularly distressed that K'Ehleyr had not taught the child anything of Klingon tradition before her death. His distress was made even more acute by Alexander's continued insistence that he had no desire to become a warrior. (TNG: "Reunion")
After Alexander came to live on the Enterprise, Worf was shocked to discover his son lied often and even stole objects. Despite his efforts to teach his son the values of Klingon society through traditional stories, such as the story of Kahless and Morath, Alexander did not take readily to the lessons. For a brief time, Worf considered sending Alexander away from the Enterprise to a Klingon school. Eventually, he decided against this, unable to part with his son, and offered Alexander the greater challenge of remaining onboard with him. (TNG: "New Ground") Still, it was the thought of his son that caused Worf to abandon thoughts of ritual suicide in 2368 and choose a risky surgery when he was paralyzed in an accident. (TNG: "Ethics")
In 2372, Worf brought an image of Alexander to starbase Deep Space 9 when he was stationed there. (DS9: "The Way of the Warrior") However, Alexander's relationship with Worf had not improved and he elected to live on Earth with the Rozhenkos rather than join his father on DS9.
That decision haunted both Alexander and his father. Alexander felt that, because he had not been the son that Worf wanted, he had been rejected, and Worf acted as if he had no son. This rejection continued to divide father and son when Alexander came aboard the Rotarran. He declared that he had no family or House and that any honor earned would be his own. Worse, his obvious lack of combat skill and previous declarations to never be a warrior led Worf to accuse him of being ill-suited for life during the war, and eventually tried to transfer him off the ship. Alexander refused, and the confrontation between the two was only resolved after the rest of the Rotarran crew began to accept Alexander. (DS9: "Sons and Daughters")
Not long after, the two continued to mend their relationship, when Worf asked Alexander to act as his Tawi'Yan, or swordbearer, during his wedding to Jadzia Dax. Alexander was honored, even more so because it was clear that the couple had altered their plans in order to include him in the wedding before he transferred to the Ya'Vang. (DS9: "You Are Cordially Invited")
During his stay on the Enterprise-D, Alexander looked up to Counselor Troi, and Worf had considered her to be the closest thing to a mother that Alexander had. Worf asked the Troi of an alternate quantum reality to be Alexander's Soh-chIm, which meant that, if anything were to happen to Worf, Troi would take custody of Alexander. (TNG: "Parallels")
The elder Alexander, as K'mtar, suggested to the younger Alexander that he had female cousins around his age on Qo'noS, possibly the daughters of Kurn, as K'mtar said he had no male heirs. (TNG: "Firstborn")
Alternate realities and timelines
In 2370, when Worf returned from a bat'leth tournament on Forcas III, Worf encountered a quantum fissure and began switching places with other versions of himself in alternate quantum realities. In some of the realities experienced by Worf, Alexander didn't exist. (TNG: "Parallels")
In 2410, Alexander traveled back in time forty years into the past, made contact with Worf and Alexander, posing as K'mtar, gin'tak to the House of Mogh. In an attempt to change history, he tried to convince Worf that his young counterpart needed to be trained in the ways of a Klingon warrior. When it became apparent that his counterpart was not willing to do so, however, he attempted to kill him, only to be stopped by Worf. He explained to Worf that, in his time, Worf had been assassinated on the floor of the High Council, due to Alexander's attempts at bringing peace to the Empire. Wishing to prevent this future, he had traveled back in time in an attempt to ensure that his counterpart would not grow up to be a diplomat, but rather a warrior who could fight at his father's side. Worf told him that, now that he had disrupted the flow of history, his death was no longer a certainty, and that he would be proud of his son no matter what path he chose to follow. After hearing these words, the adult Alexander departed, but not before expressing his love for his father. (TNG: "Firstborn")
Alexander was portrayed, in all, by five different actors: Jon Steuer ("Reunion"), Brian Bonsall (seven episodes from TNG Season 5 through TNG Season 7), James Sloyan ("Firstborn"), unknown actor (in a photograph: "The Way of the Warrior" and "Sons and Daughters"), and Marc Worden ("Sons and Daughters", "You Are Cordially Invited", and in photograph: "Change of Heart").
According to the call sheet, Alexander's makeup in The Next Generation episode "Cost of Living" was applied by makeup artist Tania McComas.
For the adult alternate future version of Alexander, Rick Berman and Michael Piller were hesitant to cast James Sloyan in the role in "Firstborn", coming as it did so soon after the actor's first appearance as Doctor Mora Pol in the DS9 episode "The Alternate". However, Jeri Taylor convinced them that the Klingon makeup would hide this fact, making Sloyan less recognizable. (Star Trek: The Next Generation Companion (2nd ed., p. 292))
As was also seen with another Klingon, Toral, this serves as an example of the phenomenon commonly referred to as Soap Opera Rapid Aging Syndrome. Being portrayed by four different actors over an eight-year period, the presentation of Alexander appears to establish that Klingon youths mature more quickly than Humans do.
In his first appearance in the mid-Season 4 episode "Reunion", Alexander was described in the script as "a Klingon boy", specifically, "the boy should look about five human years old." It should be noted that Alexander was conceived a year and a half prior, near the end of TNG Season 2. The Alexander's future self (in "Firstborn") from recalled that he had been three at the time of his mother's death, alluding to the fact that one Earth year was roughly equal to about three Klingon years.
His later appearances, beginning in mid-Season 5 through Season 7, he grew at a "normal" rate. His age was not specifically addressed in any of these episode's scripts, with exception to a note in the mid-Season 7 episode "Firstborn", which stated that his friend, Eric Burton, as "about Alexander's age"; Burton was previously established in the script for "Masks" as being twelve years old.
Alexander then served on the Rotarran (in DS9), appearing to be the size of a mid-teenager, despite actually being age eight. In fact, according to the script, he was described both a "whiskerless youth" and as a "tall, thin, beardless young Klingon [...] on the cusp of manhood." Ronald D. Moore directly addressed the seeming age discrepancy while talking about "Sons and Daughters": "We're pegging Alexander as being roughly the equivalent of a thirteen to sixteen-year-old Human male, although his actual age is much younger. Hey, Klingons mature faster, okay?" (AOL chat, 1997)
From an alternate production standpoint, Steve Oster explain that "[t]he role demanded a lot of time on the set. And the amount of time you have with a minor is very restrictive. Add to that the fact that Klingon actors need to go through three hours of makeup in the morning, and suddenly you have very little time with your actor. So his age was important. Also, we kept in mind the fact that if the actor was too young, Worf would seem too harsh. He'd come off like an abusive father, rather than a father who wants the best for his son." (Star Trek: Deep Space Nine Companion (p. 490))
Alexander was further referenced in the first draft script of the DS9 Season 4 episode ""Body Parts"", where Worf remarked that, since he was sent back to Earth, "He is happier. I am happier, and there is much less noise."
The novel A Time for War, A Time for Peace established that, upon Worf's return to Starfleet, he nominates Alexander to succeed him as Federation ambassador to the Klingons. When Alexander asks why, Worf simply tells him that he once had a vision of Alexander's future (referencing "Firstborn") and Worf says Alexander's service to the galaxy will be one worthy of song. Alexander also appears in the two novels of Star Trek: Deep Space Nine - The Left Hand of Destiny.
In Star Trek Online, set in 2409, players of the KDF faction encounter Alexander (under his "K'mtar" alias) on Rura Penthe, where he was imprisoned while attempting to discover a conspiracy against the House of Martok. With the player's aid, Alexander discovers that the House of Torg, whose members included the warden of Rura Penthe, were the masterminds of the conspiracy, aided by Romulan agents of the Tal Shiar. After Alexander and the player bring the evidence to the Klingon High Council, Chancellor J'mpok discommendates Torg and his entire House on the spot. When Torg attempts to kill Worf in revenge, Alexander sacrifices himself to save his father, thus preventing the fate that K'mtar had warned of in "Firstborn".