(covers information from several alternate timelines)
Nero was a Romulan miner originating from the 24th century, and the captain of the mining vessel Narada. Following the destruction of Romulus in 2387, Nero sought vengeance against those he felt were responsible, ultimately resulting in his being transported back in time to 2233.
Nero's actions in the past resulted in the creation of an alternate reality. In this reality, Nero was responsible for the destruction of the USS Kelvin as well as the death of its senior officer, Captain Richard Robau. George Kirk's kamikaze strike against Nero's ship, as a result of Nero's kill-or-be-killed dilemma, altered the upbringing of his son, James T. Kirk, who, in this timeline, did not join Starfleet until 2255.
Nero was later responsible for the destruction of the alternate reality's Vulcan, which resulted in the deaths of Amanda Grayson and the majority of the Vulcan race. Nero also attempted to destroy this timeline's Earth, but his plot was foiled by Jim Kirk and the crew of the USS Enterprise.
24th century origins
Nero was married and was about to become a father, but his wife and their unborn child were killed when Romulus was destroyed by the supernova of the Romulan sun in 2387. Nero was off-planet when the disaster occurred, but he witnessed the event firsthand.
Grief-stricken and madly seeking revenge, Nero placed the blame for his people's demise on Ambassador Spock, who had promised to prevent the disaster, and the Federation, which rescinded its offer to aid in evacuations following an attack on Mars by rogue synths in the mid-2380s. Spock, piloting the Jellyfish, was able to extinguish the supernova by using red matter to create a black hole which absorbed the exploding star, but before he could escape, he was intercepted by Nero, now in command of a technologically-advanced Narada and styling himself "last of the Romulan Empire". Both ships were pulled into the black hole, with the Narada going in first. (Star Trek; PIC: "Remembrance")
Arrival in the 23rd century
- Main article: Attack on the USS Kelvin
The Narada emerged 75,000 kilometers away from the Federation-Klingon border 154 years in the past, on stardate "2233-04". There, the Narada encountered, attacked, and severely damaged the Federation starship USS Kelvin. Seeking information as to the whereabouts of Spock, Nero had his second-in-command, Ayel, contact the Kelvin and demand that the ship's commanding officer, Richard Robau, board a shuttlecraft and come aboard the Narada. Robau was unfamiliar with Spock, however, and when he informed Nero of the current stardate, Nero killed Robau with his Teral'n.
Nero then launched a second attack on the Kelvin, now under command of Robau's first officer, George Kirk. Kirk used the Kelvin's weapons to prevent Nero from destroying the shuttles departing the Kelvin, ultimately sacrificing himself by ramming the Kelvin into the Narada. Kirk's actions saved eight hundred lives, including his wife, Winona Kirk, and their newborn son, James, but he was unable to destroy the Narada or Nero.
Nero spent the next twenty-five years awaiting the arrival of Ambassador Spock, plotting his vengeance against him and the Federation. Near the end of those twenty-five years, Nero was involved in an attack on a Klingon prison planet and, using the Narada, destroyed 47 Warbirds. During his time on the prison planet, Nero sustained an injury to his right ear.
Attack on Vulcan
- Main article: Destruction of Vulcan
Nero's goal was to ensure a future for Romulus that was completely free from the Federation. When Spock arrived through the black hole in 2258, Nero was waiting for him. He captured Spock's ship, which still had an entire compartment full of red matter. Rather than kill Spock, however, Nero marooned the elderly ambassador on Delta Vega so he could witness the destruction of Vulcan from the planet's surface.
With the red matter now in his possession, Nero attacked Vulcan, using the Narada's extending drill platform to burrow to the planet's core. A fleet of seven Federation starships arrived to assist Vulcan, unaware the planet was under attack. They stood no chance against the advanced Narada, however, and Nero easily and quickly destroyed them all. When another Starfleet vessel arrived, Nero ordered that it be destroyed as well.
However, after a brief attack, Nero recognized the vessel as the Enterprise. Knowing that a younger Spock served aboard the Enterprise, he ceased his attack on the vessel, wanting this era's Spock to see the destruction of Vulcan as well. He contacted the Enterprise and demanded that its captain, Christopher Pike, come aboard the Narada via shuttlecraft – the ship's transporters were inoperable as long as the drill was active. Pike complied, but only to allow a team consisting of James Kirk, Hikaru Sulu, and Chief Engineer Olson to space-dive onto the drilling rig and disable it so the Enterprise could get a signal through to Starfleet, informing them of the attack.
Though Olson had been killed during the mission, Kirk and Sulu were successful in sabotaging the drill, but not before Vulcan's core was breached. Nero released a canister of red matter into the planet's core, creating a black hole at the center of Vulcan which devoured the planet and killed the vast majority of the Vulcan race, as well as Spock's mother, Amanda Grayson. Following the planet's destruction, the number of remaining Vulcans was estimated to be less than ten thousand. Nero's mass genocide had turned the once-thriving Vulcans into an endangered species.
Attack on Earth and downfall
- Main article: Battle of Earth
Nero's next target was Earth, the core of the United Federation of Planets. Before he could attack Earth, he required the Starfleet codes which would allow him to disable the planet's defenses. He had captured Captain Pike for this purpose, and although Pike refused to cooperate willingly, Nero forced him to talk with a Centaurian slug.
With Starfleet's defenses no longer a problem, Nero set a course for Earth. As Nero prepared to attack Earth, however, Kirk and Spock were able to beam aboard the Narada from the Enterprise, which used the magnetic field of Saturn's rings to remain invisible to the Narada's sensors. Nero confronted Kirk, who was searching for Captain Pike. While fighting Kirk, Nero told the young officer that he recognized him from Earth's history and that the Jim Kirk he read about "was considered to be a great man… but that was another life."
Nero was preparing to kill Kirk when he received word that Spock had stolen the Jellyfish and used it to destroy the drill, which had already begun boring into Earth. Furious that his plans to destroy the Federation were falling apart, he called out Spock's name in anger. Nero left Kirk to Ayel and went to the bridge of the Narada. There, Nero hailed Spock and said he should have killed him back at Vulcan. Incensed at Spock's response, he quickly ordered all weapons to fire at the Jellyfish. The fact that the ship's destruction would have ignited the red matter didn't matter; he wanted nothing more than to kill Spock. Spock took the Jellyfish to warp to get out of the Sol system, and Nero quickly followed.
In an isolated area of space, Spock set the Jellyfish on a collision course with the Narada. Nero desperately ordered his crew to "fire everything." However, before Nero's fire could destroy the Jellyfish, the Enterprise emerged from warp and destroyed his torpedoes with phaser fire, leaving the Narada defenseless against Spock's attack. After Kirk (who had killed Ayel), Spock, and Pike were transported back to the Enterprise, Nero watched in despair as the Jellyfish collided with the Narada, igniting the red matter.
The resulting black hole ripped through the Narada, cutting it in half. Aboard the bridge, Nero answered the hails of Captain Kirk aboard the Enterprise, who offered his assistance. Embittered and enraged that the people he loathed above all offered him "assistance", Nero furiously refused the offer, saying he would rather watch his homeworld be destroyed a thousand times and die in agony than accept the assistance of the Federation. Kirk obliged and ordered the Enterprise to fire on the Narada. Nero remained on the bridge as he observed the ship collapsing around him and closed his eyes as he resigned to his fate. Within seconds, the Narada was consumed by the black hole, taking Nero and every remaining crew member aboard with it. (Star Trek)
Nero and the Narada's very presence in 2233 created the alternate reality, causing divergences both immediate (the destruction caused by the ship) and unrelated (Pavel Chekov's date of birth, for example).
After Vulcan's destruction, Spock led the survivors to settle on the New Vulcan colony. For stopping Nero from destroying Earth and the rest of the Federation, Kirk was promoted to captain to relieve Pike of command of the Enterprise. Pike was promoted to admiral. (Star Trek)
Admiral Alexander Marcus set about militarizing Starfleet to better defend the Federation. Marcus' main concern was not the Romulans, but the belligerent Klingon Empire. Section 31 searched for potential weapons and discovered the SS Botany Bay, and revived Khan Noonien Singh to design weapons to prepare for the imminent conflict. A year later, Khan had turned on Starfleet, and committed acts of mass murder and destruction in London and San Francisco before being placed in stasis once more. At a memorial service, Kirk, having suffered Nero and Khan's schemes, reminded his fellow officers that Starfleet's ideal was not to seek revenge on their enemies, but to be peaceful explorers. (Star Trek Into Darkness)
"Kill him? I'm not gonna kill him. I'm gonna make him watch."
- - Nero to Ayel (Star Trek)
"Hi Christopher, I'm Nero."
- - Nero to Christopher Pike when introducing himself. (Star Trek)
"I chose a life of honest labor, to provide for myself and the wife who was expecting my child. I was off-planet, doing my job while your Federation did nothing, and allowed my people to burn while their planet broke in half. And Spock, he didn't help us. He betrayed us!"
- - Nero to Christopher Pike (Star Trek)
"No, you're confused, you've been misinformed! Romulus hasn't been destroyed, it's out there right now! You're blaming the Federation for something that hasn't happened!"
"IT HAS HAPPENED! I WATCHED IT HAPPEN, I SAW IT HAPPEN! DON'T TELL ME IT DIDN'T HAPPEN!"
- - Christopher Pike and Nero, about Romulus' destruction. (Star Trek)
"When I lost her, I promised myself retribution. And for twenty five years I planned my revenge against the Federation, and forgot what it was like to live a normal life. But I did not forget the pain. It's a pain that every surviving Vulcan now shares. My purpose, Christopher, is to not simply avoid the destruction of the home that I love, but to create a Romulus that exists free of the Federation. You see, only then will she be truly saved. That is why I will destroy all the remaining Federation planets, starting with yours."
- - Nero trying to justify his actions to Christopher Pike. (Star Trek)
- - Nero on Spock commandeering the Jellyfish (Star Trek)
"I want Spock dead now!"
- - Nero to a Romulan officer. (Star Trek)
- - Nero on seeing the Jellyfish set a collision course. (Star Trek)
"I would rather suffer the end of Romulus a thousand times. I would rather die in agony than accept assistance from you!"
- - Nero's response to Kirk's suggestion that he surrender peacefully. (Star Trek)
Nero was played by Eric Bana.
In the script of Star Trek, Nero seemed significantly more compassionate to Humans than he is in the final version of the film, at one point commenting, "It's not the fault of the human race that Starfleet chose Earth as its center. You're a more noble race than my fallen cousins. I'll take no pleasure in your extinction." The script also had Nero kill Ayel prior to the Battle of Earth, and Nero's scripted last words were "Forgive me… Romulus…" 
In the film, Ayel addresses Nero as "Prod". In a deleted scene in which the Narada is surrounded by a Klingon fleet, the subtitles created for the scene translate "prod" as "Commander." However, in the audio commentary for the film, the writers state that "Prod" was intended to mean "Praetor." In all other instances, Nero is referred to as "Captain." Based on the use of "Commander" in both The Next Generation and Deep Space Nine episodes to refer to Romulans (and Vulcans) in command of military vessels, it may be that the Romulan understanding of the word has a specifically civilian connotation, while "Commander" refers to a military role.
In the prequel comic Star Trek: Countdown, Nero's backstory is expanded upon. According to the series, Nero was initially in league with Spock, and attempted to help him stop the supernova threatening Romulus. When Vulcan declined to assist Romulus by handing over the technology necessary to produce red matter, Nero blamed Spock and Vulcan after the supernova destroyed Romulus, believing it was a ploy to claim Romulan territory. He claimed his teral'n from the Romulan Praetor, whom he killed for ignoring Spock's warnings about the supernova. His knowledge of James T. Kirk's past is revealed as having been gained when he consulted the non-restricted databanks onboard the USS Enterprise-E during the initial phase of his quest to stop the explosion that would destroy Romulus. An explanation is also given for the tattoos on Nero and his crew:
- "There was a tradition on Romulus that when a loved one died you would paint your grief upon your skin. Ancient symbols of love and loss. In time the paint would fade, and with it the period of mourning. Life would go on. We paint these symbols on our skin now. But we burn them deep. So that they will never fade. Because life does not go on. We died with our friends. We died with our families. We died with Romulus. And all that is left is revenge."
In the novelization of 2009's Star Trek by Alan Dean Foster, Nero states that his formal name resembles "Oren" ("Ŏ'ŗên"), but is difficult for Humans to pronounce. The novel reiterates that Nero believed the destruction of Romulus was part of a conspiracy perpetrated by the Federation, and that any attempt to warn of the supernova in the past would therefore be futile. It is also suggested that if Nero had succeeded in destroying the Federation, he would have used any remaining red matter to create a black hole and consume the star before it could go supernova. Additionally, Nero states that the annihilation of the Federation would allow the Narada crew to return to Romulus as warriors rather than simple miners.
The 25 year gap to Nero's whereabouts in Star Trek is the setting for the comic series Star Trek: Nero, the follow up to Star Trek: Countdown. Its ideas incorporate the deleted scenes of Nero's imprisonment on Rura Penthe, explaining that despite his numerous escape attempts, he and his crew are kept alive as their mining benefits the Klingons economically. Nero becomes telepathic, training the Vulcan side his people had locked away, enabling him to communicate with his Borg-modified ship and later V'ger to calculate where and when Spock will arrive. The Klingons are shown to also be unable to unlock the technology behind the Narada, preventing them from gaining a significant technological advantage and finding a way to counter Nero's ship, thereby later leading to the massacre of 47 Klingon ships when they come up against him, explaining the backstory behind the mysterious report intercepted by Uhura as shown in the 2009 film. A Targ was revealed to be responsible for biting off his right ear tip and creating the scars on that side of his head.
In issue fifteen of the Star Trek: Ongoing comic series, a version of Nero is flung back into the mirror universe's past instead of the prime reality. After the Terran Empire conquers the Klingons, Commander Kirk finds Nero on Rura Penthe, and avenges his father by breaking his neck.
The last story arc of the Star Trek: Boldly Go comic introduced a reality where Nero was instead briefly defeated at Andoria by Kirk preventing his destruction of Vulcan, but then later regrouped with the Romulan Empire to destroy Earth.