Recruited for the Unity Division in Uncanny Avengers (1st series) #1.
Havok formerly wore an anti-grav harness for flight and a containment suit that monitored his energy output. As a member of the Australian X-Men, Havok was once rendered invisible to all forms of electronic detection. He became Havok in X-Men (1st series) #58.
Mutant X was actually only the title of the book, it was never used as a codename for Alex inside the issues. He was constantly refered to as Havok.
Havok's body was destroyed fighting O*N*E in Uncanny X-Men (5th series) #22. He has since appeared on Krakoa in House of X #6, presumably as a result of the Resurrection Five's efforts.