Karl Lykos was the son of an explorer's guide. As a teenager, he accompanied his father to Tierra del Fuego as the elder Lykos guided a weathy client named Mr. Anderssen and Anderssen's young daughter Tanya. While defending Tanya from mutant pterodactyls, Karl was bitten by one of the creatures. During his recovery, he discovered that he could now drain the life-force of other organisms. He found himself repeatedly tempted to use his new power.
When Karl's father died, Mr. Anderssen took Karl into his home in thanks for rescuing Tanya. As the years passed, Karl and Tanya fell in love. But Tanya's wealthy father would not allow her to date Karl because of his lack of wealth. In an effort to win Mr. Anderssen's support, Karl went to medical school and became a physician. He treated patients through hypnosis, but secretly robbed them of energy at the same time.
Dr. Lykos was a colleague of Professor Charles Xavier, and first encountered the X-Men when they sought treatment for Havok. When Lykos absorbed energy from Havok, there was a horrible side-effect: he transformed into a vampiric, pterodactyl-like monster. He named himself Sauron, after J.R.R. Tolkien's villain (also reminiscent of the word saurus, Latin for lizard), and battled the X-Men. But when he realized that his transformation would threaten Tanya, he fled to Tierra del Fuego. Without energy to absorb, Sauron turned back into Karl. When Tanya tracked him down, Karl threw himself off a cliff to avoid harming her.
Presumed dead, Karl actually survived, merely unconscious on a ledge below. He journeyed to the Savage Land and survived in human form by only draining less developed animals. He befriended Ka-Zar and used his medical skills over many months to care for Ka-Zar's allies. But when several X-Men were stranded in the Savage Land, Lykos was overwhelmed with the desire to absorb the powerful life energy of mutants. He transformed into Sauron once again after absorbing Storm's energy. He reverted back to human form during a battle with the X-Men, and Ka-Zar explained that Lykos was an ally.