The X-Men
Xavier tracks down Lucifer, whose heartbeat is rigged to a thermal bomb, and the X-Men must prevent the Avengers from defeating him to save the world.
Collects The X-Men #1-23. The original Stan Lee and Jack Kirby X-Men -- the very beginning of mutantkind in the Marvel Universe.
Collects The X-Men #1-31, X-Men: The Early Years #1. Stan Lee and Jack Kirby original X-Men from their 1963 debut.
Collects The X-Men #9, The X-Men vs. the Avengers #1-4. X-Men and Avengers clash, including the original 1965 crossover in X-Men #9.
Collects The X-Men #9, The X-Men vs. the Avengers #1-4. X-Men vs. Avengers — the classic 1987 limited series over Magneto fate.
Collects X-Men #1-13. The earliest X-Men adventures by Stan Lee and Jack Kirby — where it all began in 1963.