Michael "Mike" Jonas was a Human male alive during the late-24th century. Maquis resistance fighter turned provisional Starfleet crewman, Jonas later betrayed his new crew on the USS Voyager to the Kazon.
Jonas joined the Maquis during the early-2370s. He served under Chakotay on the raider Val Jean until 2371, when he and the rest of the Maquis crew were pulled into the Delta Quadrant by the Caretaker and his array alongside the Federation starship USS Voyager, which had been in pursuit of them through the badlands.
With the hostile Kazon species closing on the station, Voyager's Captain Kathryn Janeway elected to destroy the array to prevent the technology falling into the wrong hands. The Val Jean was destroyed in the battle and the Maquis crew, including Jonas, transported to Voyager.
Life on Voyager
Unlike the other Maquis crew who gradually adjusted to their new situation, Jonas secretly objected to the Starfleet rules and procedures that Captain Janeway insisted on upholding. In 2372, the death of fellow Maquis Kurt Bendera in battle with the Kazon, caused Jonas to question her policies, specifically about the sharing of technology with other races in exchange for their assistance and protection. After witnessing his friend Hogan attempt to convince chief engineer B'Elanna Torres to contact Seska, who had defected to the Kazon-Nistrim, Jonas, behind the captain's back, secretly opened communications with Culluh's aide Rettik, intending to negotiate on his own terms with Seska. (VOY: "Alliances")
When Tom Paris successfully crossed the transwarp threshold, achieving warp ten, Jonas transmitted details of Voyager's new technology to Rettik. (VOY: "Threshold") Jonas also informed the Kazon-Nistrim, this time via a new contact named Lorrum, when Voyager encountered Dreadnought, a Cardassian missile. (VOY: "Dreadnought")
Jonas sent his secret transmissions via Voyager's power grid, encoded in waste energy from the ship's propulsion systems, making the covert reports almost indistinguishable from galactic background noise. However, Lieutenant Tuvok did detect the transmissions, but was unable to locate the source. He reported this to Janeway and together they assembled a plan to expose the traitor.
They secretly recruited Tom Paris to act as an agent provocateur. Pretending to be dissatisfied with life aboard Voyager, Paris' behavior became more and more erratic over the course of several weeks to the extent of striking Chakotay while on the bridge. As a consequence of his planned behavior, Paris ultimately left Voyager to join a Talaxian convoy.
The plan worked and Jonas informed Lorrum of what he thought was growing dissent among Voyager's crew. When he was asked to sabotage the ship's warp coils, though, Jonas declined, insisting Seska must contact him personally with such a request.
A short time later, Jonas spoke with Seska, telling him that all of his helpful messages had been brought to her. She went on to coerce Jonas into participating in a plan of hers, which would include the Nistrim waiting for Voyager at a planet called Hemikek IV. (VOY: "Lifesigns", "Investigations")
Putting Seska's plan into motion, Jonas sabotaged Voyager by forcing the magnetic constrictors out of alignment, which caused a plasma overload that had to be vented via the warp nacelles, thereby damaging the ship's warp coils. The plan was that this would force Voyager to head to the Hemikek system and land on Hemikek IV in order to seek materials to complete repairs. Kazon-Nistrim forces would then storm the ship on the ground.
Meanwhile, Neelix became suspicious of Paris' departure from the ship and commenced his own investigation. Janeway and Tuvok quickly acted to stop him from exposing their deception, bringing him into the plan, and asked him to announce that they had found Paris to be the traitor. Jonas fell for the ruse and contacted Seska about these events, after which Kazon-Nistrim forces attacked the Talaxian convoy and kidnapped Paris. Recognizing Paris' value, Seska tried to convince him to join them, but instead he broke into their computers, learned the identity of the traitor, and then escaped. He was able to transmit the information to Voyager, just as Jonas was preparing to sabotage the ship's weapons. Neelix continued his own investigation and also discovered Jonas' treachery, which led to Neelix being trapped in main engineering with Jonas in an attempt to prevent his sabotage. It was after struggling with Neelix that Jonas was killed, as he fell into a plasma fire near Voyager's warp core. (VOY: "Investigations")
The next year, Michael Jonas was recreated in a holographic program aboard Voyager called Insurrection Alpha, which had originally been created by Tuvok as a tactical simulation of a Maquis mutiny on the ship. (VOY: "Worst Case Scenario")
Michael Jonas was played by actor Raphael Sbarge.
Although he had watched both Star Trek: The Original Series and Star Trek: The Next Generation, Sbarge nearly turned down the role of Jonas due to character's lack of depth. Despite being very interested in appearing on Star Trek, Sbarge at first wanted to take a chance by waiting and finding out if a more substantial part would be offered to him. "My agent said, 'No, no, no. They're developing this guy and want to do something with him,'" the actor recalled. "I said, 'OK, it'll really be a kick to be on the show' [...] After I got the part I wrote the casting director a letter and said, 'You know, you get a lot of jobs in your life, but how many people can say that they've worked on Star Trek? What a wonderful opportunity to have this type of experience.' I really meant that and was looking forward to working on the series." (TV Zone, Special #29, pp. 24-25)
Portraying Jonas involved some difficulties for Raphael Sbarge (such as accidentally hurting himself, multiple times, while filming "Investigations"). "The most difficult thing about the part [...] is the technobabble," he noted. (TV Zone, Special #29, pp. 25 & 26) Sbarge found some of his lines so difficult he had to go over them again and again. "What happened was that the words that they made up were so difficult to memorize, and I would arrive literally white-knuckled on set, having run through them all night in my sleep, trying to make sure that I had them, because they were just the most jabberwockian combination of things. So what happened was, he gave me some memorization tools so that I could find my way through it. That was the scariest part of it. But I remember at one point actually having to resort to writing something on a card because I just couldn’t get it, and I placed it carefully on part of the engineering set so that I could look over and grab it. Of course, I don’t remember what it was. I just remember that it was just impossible to learn!" 
Sbarge nonetheless thoroughly enjoyed playing the role and making Jonas a recurring character. "They developed Jonas for a while and were trying to figure out exactly which way they wanted to go and how to expose him," Sbarge explained. "Apparently, it's unusual to develop a character like this over five episodes because of how things work in syndication." (TV Zone, Special #29, pp. 25 & 26)
Raphael Sbarge had some of his own ideas about Jonas. Concerning the character's motives, Sbarge reckoned, "He clearly saw that Voyager was going into some very dangerous territory without any sort of help. I think he began to feel that they were surrounded by the Kazon and would eventually be blown to bits unless they made some genuine and serious moves towards making peace or creating a balance with them. In his own way, at least initially, I think he did what he did from a sort of benevolent point of view. It wasn't completely good for everyone because it was really self-motivated but I don't think he intended for it to get as bad as it did. He eventually got himself in a position where Seska was blackmailing him and then he was stuck. When you lie you have to cover your lies. One lie leads to another lie and that's what happened to Jonas. He got in too deep." Regarding Jonas' familiarity with Seska, Sbarge reckoned, "My sense was that they probably knew each other when they were young and maybe there was even a romantic thing that went on there. That was my thought. Whether that is what was in the producers' minds, I don't know," he laughed. (TV Zone, Special #29, p. 24)
Raphael Sbarge also found the character of Jonas was popular with fans. In a 1998 interview, he noted, "I just received a whole bunch of fan mail from viewers who saw the episodes I was in." Of all of the episodes he did, Sbarge rated "Investigations" his favorite. (TV Zone, Special #29, pp. 26-27)