Alexander Summers is Scott Summers's only brother, separated from him and unknowingly raised as Mr. Sinister's pawn to take advantage of Alex's mutant powers of cosmic radiation absorption and emanation of it in the form of powerful plasma blasts. His immense power, combined with his standoffish attitude, have often put him at odds with his brother and the rest of the X-Men, but Havok has remained a proven ally to the heroes' cause.
Some time before the Pulse, which brought the mysterious compound Isotope-8, hit Earth, Havok joined the Hellfire Club, possibly to work against them from the inside. When that group planned to transform the Living Pharaoh into the Living Monolith, he tried to stop it for a second time. As the Hellfire's protection prevented him from accomplishing his goal, Havok decided to ask help to S.H.I.E.L.D.'s Alliance.
The Hellfire Club used Havok as a conduit of cosmic energy to empower the Living Pharaoh's transformation along Isotope-8. After being defeated, the Living Monolith didn't return to his normal form due to the use of Iso-8 in his transformation, but he was held captive by S.H.I.E.L.D., where Beast and other mutant scientists worked on him.
In the end of the conflict, Havok decided S.H.I.E.L.D. could use his help as he used theirs, joining their Alliance.