The X-Men #124

From 1979's Uncanny X-Men #124, this Dave Cockrum and Terry Austin cover crackles with team-on-team tension as Cyclops and Storm find themselves squaring off against a rampaging, armored Colossus — the cover text making the stakes plain: "He was one of the X-Men — now, he's the power-mad Proletarian!" Cyclops pleads "Don't you understand, Colossus? We're your friends!" while Storm recoils from his grip amid explosions and churning water, with additional teammates visible in the background inset. Inside, Chris Claremont and John Byrne deliver "He Only Laughs When I Hurt!" — a creative team at the height of their celebrated run together.