8 X-Men Who Became Avengers
7. X-23
X-23's first appearance was actually in the X-Men Evolution cartoon and her popularity afforded her a translation over to the Marvel comics universe. Genetically engineered using Wolverine's DNA, X-23 was designed, raised and trained to be the perfect assassin, controlled by a pheromone labelled the "Trigger Scent" that would send her into a murderous frenzy.
After escaping the facility that held her captive, X-23 found her way to the X-Men and Wolverine himself. Since this point, X-23 has made efforts to put her past behind her and cement herself as a valuable member of the X-Men, eventually taking up the mantle of Wolverine following Logan's death.
Due to her reliability, skill and the guidance of Wolverine she was enrolled into the Avengers Academy and remained there for a long while, even during the events of Avengers Vs. X-Men. X-23 was one of the remaining students who were registered as associate-level Avengers at the end of Avengers Academy.