750,000 years ago, Alars, a member of the Eternals of Earth, a cosmic-powered sub-species of humanity, departed Earth after his brother Zuras became the Eternals' leader. Alars journeyed to Titan, a moon of Saturn, where a band of exiled Eternal settlers had slaughtered each other in war. Alars married the only survivor, a young woman named Sui-San, and they transformed Titan into a paradise. Alars ruled the Eternals of Titan as Mentor and created ISAAC, a computer which serviced all of Titan's technological needs.
The youngest son of Mentor and Sui-San, Eros had the natural ability to excite pleasure in others, but his power had no effect upon his mutant older brother, Thanos, who worshiped the cosmic embodiment of Death and led an army against Titan. During this assault, Thanos killed and dissected Sui-San, trying to learn why he was born different. While his brother was captivated by Death, Eros loved life, and began visiting other systems for adventure and romance. Eros even visited Earth at least once, and was remembered in Earth's legends. He had many lovers, but his only steady relationship was with the prostitute Heater Delight. Eros later helped Heater escape more than one possessive master, including Dark Roger and Axel the Rescorlan. While she was the property of Pro-Boscis the Procurer, Heater kept Eros from saving her because she didn't want his face damaged; she instead manipulated Pip the Troll into saving her.
In recent times, Thanos conquered Titan with another army, slaughtering most of the Titans until Mentor and Eros were the only remaining resistance. Thanos, now seeking the Cosmic Cube, brought Rick Jones to Titan to learn its location. Rick was freed by Mentor, Eros and the Kree warrior Captain Marvel, who had been bonded to Rick; together, they battled Thanos' armies and drove off his lieutenant on Titan, the Super-Skrull. Mar-Vell ultimately bested Thanos by seemingly destroying the Cosmic Cube, and Mentor and Eros were able to rebuild Titan. Mar-Vell became a close friend of the Titans after his help.
Thanos, however, had secretly left behind a programming virus compelling ISAAC to act on his behalf. Creating lieutenants for itself, ISAAC took the Titans captive. One lieutenant, Elysius, was attracted to Eros, but she later shifted her affections to Mar-Vell and changed sides when he came to Titan to oppose ISAAC. Mar-Vell ultimately drove Thanos' programming from ISAAC, saving Titan. Mar-Vell soon succumbed to cancer, spending his last days on Titan. Eros was devastated by the loss, and remained close to Elysius in the days that followed. Elysius eventually had ISAAC help her create a son from Mar-Vell's DNA; she named the child Genis. He was raised to believe that Eros was his father, and Eros helped maintain the facade until Genis' accelerated coming of age.
Longing for new adventures, Eros visited Earth again and encountered the Avengers battling the Plantman. Eros asked to join their team and was accepted as an Avenger-in-training; but the Avengers were reluctant to present a man named "Eros" to the public so the Wasp rechristened him "Starfox." Eros was chagrined to meet fellow trainee Captain Marvel (Monica Rambeau), and he looked down on her, still stung by the death of Mar-Vell. Starfox learned teamwork and responsibility amongst the Avengers, but still found time to engage in several romantic liaisons, including a one-night stand with his teammate She-Hulk. The team also valued Starfox for his scientific knowledge as he was serving on a roster devoid of the Avengers' usual scientific geniuses. After many of the Avengers were taken to Battleworld to serve in the Beyonder's "Secret Wars," the Vision became the Avengers' chairman and promoted Starfox to full membership to fill out the roster. Starfox retained his standing when the other Avengers returned.
One evening, Starfox invited himself and the Wasp to a party in Soho which was held by Sersi, a member of Earth's Eternals. When Sersi was brought to the Eternals' city of Olympia to participate in a gathering of all Eternals, Starfox was brought along. In Olympia, he fascinated his Earth-bound cousins with the story of how Alars had founded Titan. Starfox participated in the Eternals' Ritual of the Uni-Mind, merging with them into a single psionic entity; but when the villain Maelstrom tried to siphon the Uni-Mind's power for himself, and the Vision and Scarlet Witch freed the Eternals from the Uni-Mind. Starfox managed to incapacitate Maelstrom with his pleasure powers, which he revealed to the Avengers for the first time. Maelstrom caused his own death by having his servant Deathurge kill him so that he could live anew in another cloned body. The Avengers subsequently thwarted Maelstrom's next plot to halt the Earth's rotation. After seeing Captain Marvel's courage in that battle, Starfox finally accepted her use of his friend's name, apologizing to her for the way he had slighted her.
The Avengers became embroiled in a civil war amongst the Skrulls, during which the pirate Nebula seized Thanos' starship Sanctuary II and used it to command a Skrullian fleet to destroy the planet Xandar. When Starfox confronted Nebula, she claimed that Thanos was her grandfather. Before Eros could learn more, Nebula was teleported away by the Beyonder, who had misunderstood the wish of the Xandarian survivor Firelord that Nebula be cast out of the galaxy. Starfox was determined to learn if Nebula's story was true, quit the Avengers to hunt her alongside Firelord. The pair were attacked by Super-Nova, another survivor of Xandar who incorrectly believed Nebula to be one of the Avengers, and Starfox was badly injured, but he soon recuperated and resumed his pursuit of Nebula. He finally caught up to her and helped the Avengers thwart her attempt to harness the Infinity Union, a device of the Stranger's which could grant her cosmic power.
Soon afterwards, Thanos obtained the Infinity Gauntlet (which housed the six Infinity Gems) and used it to offer the universe to Death. Thanos took Starfox hostage during the crisis so that his brother could witness his actions, but Thanos allowed himself to be beaten, not truly desiring victory in the end. Starfox continued to serve as an occasional Avenger, participating in the Avengers' mission to the Shi'ar Empire during the Kree-Shi'ar war, as well as joining the Avengers against Morgan Le Fay when she mastered the power of the Twilight Sword.
In the aftermath of that battle, Starfox befriended his fellow Avenger Tigra, and she set off into space with him to visit Deneb-VII. Tigra soon became bored of Deneb-VII, but the duo found new excitement when the universe was threatened by the Infinites, cosmic beings from another universe who had no regard for the lives of lesser beings. Starfox and Tigra teamed with Jack of Hearts, Quasar, Thor, Photon and Moondragon to face the Infinites. Starfox helped appeal to the Infinites through Eternity, the embodiment of space, and one of the Infinites ultimately chose to sacrifice itself to repair some of the damage they had done. Later, Starfox led a small army of Eternals in attacking Thanos (or possibly one of the "clones" known as the Thanosi) during his quest for the Celestial Messiah, but they were soundly defeated and Eros was cast into outer space, beaten senseless.
Starfox later confronted the time-traveler Thanatos, a version of Rick Jones from another reality intent on gathering items of power. Thanatos struck Starfox in the neck with the Spear of Destiny, causing a wound which could not be healed, then threatened to kill him unless he brought Rick Jones (now bonded to Genis) to him. Starfox was forced to comply, but Rick and Genis were able to defeat Thanatos in the end, reversing his actions. After Genis' power of cosmic awareness drove him insane, Starfox joined with Elysius, Mentor and the other Titans in opposing him; they were ultimately able to help Genis regain his sanity.