Years later, Xavier saved Scott Summers from the Living Diamond and a possible life of crime. Summers became one of the first students at Xavier’s School for Gifted Youngsters, where he took on the codename Cyclops. Subsequent recruits included Bobby Drake (Iceman), Warren Worthington III (Angel), and Hank McCoy (Beast). Together with Jean Grey as Marvel Girl, they became the original X-Men under the tutelage and leadership of Xavier as Professor X.
The X-Men received their first test when Magneto seized control of the Cape Citadel military base. Even though the team was inexperienced, the supposed Master of Magnetism was forced to flee. Their successful debut led the X-Men to be hailed as heroes, and they subsequently took on the Vanisher, the Blob, Unus the Untouchable, and Namor the Sub-Mariner. In response, Magneto recruited the Scarlet Witch, Quicksilver, Toad, and Mastermind for his own team: the Brotherhood of Evil Mutants. The Brotherhood proved to be very dangerous foes, although Scarlet Witch and Quicksilver had sympathy for humanity which prevented Magneto from destroying their rivals.
Shortly after the X-Men’s first encounter with the Avengers and Xavier’s rematch with Lucifer, the team discovered the prehistoric jungle known as the Savage Land and befriended Ka-Zar. When they returned home, Professor X’s estranged stepbrother, Cain Marko, made his debut as the unstoppable Juggernaut and attacked the group. As public opinion turned against mutants, Dr. Bolivar Trask unveiled his mutant hunting giant robots: the Sentinels. Because of their programing, the Sentinels decided that the only way to protect humanity was by controlling it. Trask gave his life to stop them, but his son, Larry, eventually rebuilt the Sentinels.
Mimic became the sixth member of the X-Men, although his personality clashes with the other students meant that his stay was a short one. The team also made a new ally when they freed Banshee from the control of Factor Three and the Mutant Master. Following Factor Three’s defeat, Xavier began making preparations to head off an invasion by the Z’nox, a powerful alien race. By chance, Factor Three’s shapeshifting operative, Changeling, approached Professor X with a desire to reform. Charles accepted Changeling’s offer and allowed him to step into the role of Xavier himself. The false Professor soon fell in battle, leaving the team to believe their mentor was dead.
Although they were officially disbanded, the X-Men remained in each other’s lives. An early confrontation with Mesmero led the team to Lorna Dane, a young woman who inherited her magnetic powers from her father, Magneto. Cyclops’ younger brother, Alex Summers, also joined the team as Havok. After his initial battle alongside the X-Men, Havok was injured and placed in the care of Dr. Karl Lykos. While Lykos was not a mutant himself, he was an energy vampire who took advantage of his patients to keep himself fed. But when Lykos drained Havok, he became a pterodactyl-like creature who called himself Sauron.
After defeating Sauron and encountering the Japanese mutant, Sunfire, the X-Men discovered that Xavier was still alive. Jean revealed that she had known all along and helped Professor X prepare for the Z’nox invasion. The final battle nearly killed the real Xavier, but the X-Men were once again able to revive their mentor. As the team returned to the Savage Land to learn about Magneto’s fate, Xavier and his former lover, Dr. Moira MacTaggert, began training a new team of X-Men: Petra, Sway, Darwin, and Vulcan, the secret brother of Cyclops and Havok.
When the first group of X-Men was captured and fed upon by the living island of Krakoa, Professor X sent the new team to save them over the objections of MacTaggert. This proved to be a disastrous decision, as the untested mutants were seemingly killed by Krakoa. Xavier used his powers to erase Cyclops’ memories of the tragedy, and he quickly assembled an international squad that included Nightcrawler, Thunderbird, Storm, Colossus, and Wolverine, as well as Banshee and Sunfire. Together, they rescued the original X-Men and sent Krakoa hurling into space.