Indicia title: X-Men, Vol. 1 No. 1; cover title: King-Size Special! X-Men™. On-sale date from 1970 Periodicals, Copyright Office, Library of Congress with a correction factor of plus 28 days.
Sources for letters credit are The Marvel Comics Index (Olshevsky 1981), The Official Marvel Index to the X-Men (Olshevsky 1987), The Official Marvel Index to the X-Men (Ward 1994), and Official Index to the Marvel Universe (Vandal et al. 2009).
The X-Men [Professor X; The Angel; The Beast; Cyclops; Marvel Girl [Jean Grey]; Iceman]; The Avengers [Giant-Man [Hank Pym]; Thor; Captain America; Iron Man; Wasp]; Lucifer (first appearance)
Synopsis
Xavier has tracked down Lucifer, who cost him the use of his legs, but finds his foe's heartbeat is rigged to a giant thermal bomb. The X-Men arrive in Bavaria and run across the Avengers who have also just arrived. The X-Men have to stop the Avengers from defeating Lucifer since by defeating Lucifer, the world will be destroyed. After Xavier gives Lucifer a mind blast that renders him unconscious, he contacts his team for help and the Avengers agree to let the X-Men clean up the current crisis on their own. Cyclops uses his eye beams to disable Lucifer's thermal bomb.
The X-Men [Professor X [Charles Xavier]; Cyclops [Scott Summers]; Angel [Warren Worthington III]; Beast [Hank McCoy]]; Marvel Girl [Jean Grey]; Iceman [Bobby Drake]]; The Stranger (first appearance); Brotherhood of Evil Mutants [Magneto [Erik Lehnsherr]; Mastermind [Jason Wyngarde]; Toad [Mortimer Toynbee]; Quicksilver [Pietro Maximoff]; Scarlet Witch [Wanda Maxinmoff]]; Charlie (first appearance)
Synopsis
Xavier detects a powerful entity has arrived on earth and sends the X-Men to investigate. The Stranger tries to acclimate himself to Earth customs but runs across Magneto and the Brotherhood. The X-Men arrive on the scene and battle the Brotherhood, but the Stranger leaves with Magneto and Toad in the conflict. Quicksilver and the Scarlet Witch decide to return home to Central Europe. The X-Men encounter the Stranger again and Xavier realizes he is an alien. The Stranger explains that he has been collecting mutants from across the universe and takes Magneto and Toad away with him into space.