Sixth Ranger Traitors in Comic Books.
- The Avengers: The Swordsman, a Villain with Good Publicity, joined The Avengers under orders from Iron Man's enemy the Mandarin to sabotage the team. After gaining the trust of most of the team, he planted a bomb in their headquarters. It was after he had a change of heart and disarms the bomb that he was found out and the team sent him packing.
- Nemesis Kid of the Legion in Legion of Super-Heroes. He joined the Legion to spy on them for the evil Khund Empire (and later became a member of the Legion of Super-Villains).
- Shun-Day was this to the Legendaries, acting as The Mole to her creator Skroa. She however become the mask and ends up saving the other Legendaries from him. Danael agreed to let her go as a gratitude, but warned her that the next time they'd meet, it'd be as enemies.
- Later subverted during the Anathos Cycle when Tenebris, Darkhell's daughter, joins the team. Her motivations for helping the heroes are selfish, she is known to love her father, and two of the Legendaries (namely Shimy and Gryf) were expecting her to betray them, to the point Shimy tried to murder her once it appeared she was of no more use. Ironically, it turned out she never betrayed the team, even when Anathos gave her the opportunity to join her after he single-handedly defeated the other heroes. After the Cycle, she has become a full-time member of the group.
- Runaways:
- Topher is introduced as a kid apparently in a similar position to the heroes, and is a little too charming and eager to get on with everyone. He turns out to be a vampire and tries to murder them all. His betrayal causes the team to be initially suspicious of Sixth Ranger Victor Mancha, especially since they know he's the son of a villain (though they don't know which one for a while) and supposedly destined to turn evil. Given that every single fricken one of them is the child of at least one, and in most cases two villains, what do ya expect?
- It's also implied to have happened on purpose, because Alex knew all along that Topher was a vampire (or at least evil) and brought him to the Hostel so that the rest of the group could end up fighting him to be toughened up.
- Star Wars (Marvel 1977) does have regulars added to the cast not infrequently. Most of them work out okay - but Shira Brie, Luke Skywalker's Wing Guard and incipient Love Interest, turns out to have been hand-picked by Darth Vader.
- Teen Titans: After the New Teen Titans formed, their first new member was Terra, a cute teen girl with a sad backstory. One year later...well, there's a reason that Terra's grand finale is called The Judas Contract. (However, the Titans didn't return to status quo; The Judas Contract also introduced Jericho, who became a long-standing member of the team.)
- Titan's Transformers: Animated Comic had a new character called Afterburn, who is one of the greatest Autobots to ever live, who cured a fatal infection and has recommendations from Ultra Magnus himself. He's really a soulless drone created by Megatron, who faked his credentials.
- In an example that would have made fans of the original series cry, Sven, one of the most popular characters of the original Voltron: Defender of the Universe series became this in the 2003-4 Devil's Due Darker and Edgier Continuity Reboot.
- Wonder Man, the first Avenger to join the team after Captain America, was one of these. An industrialist driven out of business by Tony Stark, he was approached by the Masters of Evil and offered superpowers and revenge. It wasn't until after he'd gotten his powers that the Masters revealed the catch -that his powers would kill him without regular treatments that only Baron Zemo could provide - and sent him to infiltrate the Avengers. Since Good Feels Good, though, Wonder Man discovered he preferred being a hero and ended up saving the team from the Masters' trap at the cost of his own life. (Being comics, he got better. Then worse. Then better again.)
- In Grant Morrison's run on X-Men, where the core team starts out as a Five-Man Band, Xorn isn't just a traitor, he's Magneto in disguise! (For a while, anyhow.) Change and (perhaps futile) attempts to escape the status quo were major themes in this run. The first to join the original Five-Man Band (not counting the Professor) from the sixties, Mimic, also betrayed the team.
- New X-Men: Academy X has an interesting case with this happening to both the New Mutants and their rival team at the same time. Both teams were five groups of friends short of one to make a full training squad. Icarus was added to the Hellions, whom he barely knew, because Julian convinced him to join, and Wither joined the New Mutants after he returned to school. Once the FBI tried to arrest Wither, the Hellions decided to bust him out and Icarus, realizing how horrible the consequences such act would have, contacted the New Mutants and both groups fought. Once Wither was cleared of all charges he realized who his real friends were and asked to be re-assigned to the Hellions, while Icarus jumped at the opportunity to take his spot on the New Mutants.
