||The X-Men [Professor X (Origin); Cyclops; Marvel Girl [Jean Grey]; Angel; Beast; Iceman]; Juggernaut [Cain Marko; 1st and Origin]; Kurt Marko (flashback); Sharon Xavier [Professor X's mother; flashback]
||Cerebro detects a powerful mutant and Xavier fears that he knows who it is; The X-Men prepare the mansion for an all out assault; As the mysterious villain batters his way through the mansion's defenses, Professor X tells his students his origin story and how his step-brother changed from tormenting bully to an unstoppable Juggernaut.
||Jack Kirby layouts; Alex Toth pencils
||1st two part story.
||in X-Men (Marvel, 1963 series) #67; in Marvel Masterworks (Marvel, 1987 series) #7; in X-Men: The Early Years (Marvel, 1994 series) #12; in X-Men (K. G. Murray, 1970 series) #2; in Marvel Special (Marvel Italia, 1994 series) #6