A gifted young sprinter, Delroy Garrett, Jr. won three Olympic gold medals before he was exposed as a steroid user. Stripped of his awards and livelihood, Garrett sought new direction in the Triune Understanding, a philosophical movement that preaches the fulfillment of one's innate potential by balancing various aspects of environment and self. Developing a superhuman triple-powered physique, Garrett believed the Triune teachings had unlocked his latent powers, and he became the costumed hero Triathlon while serving as a celebrity spokesman for the Triune Understanding. Aiding the Avengers against Moses Magnum, Triathlon worked well with the group, but tensions arose after unscrupulous Triune leader Jonathan Tremont began a secret smear campaign against the Avengers as part of a Triune publicity ploy, painting the Avengers as religiously intolerant and racially biased.
Unaware of Tremont's true nature and secret plans, Delroy began to believe that the increasingly hostile Avengers might be intolerant, even racist; but the feud came to an unexpected end when the Avengers' government liaison Duane Freeman-another Triune follower-convinced the Avengers to recruit Triathlon, since he was a capable hero whose visible minority status and Triune background would help defuse much of the group's negative publicity. Determined to prove the Avengers wrong about the Triunes, Triathlon joined the team. Wary of his fellow Avengers and resenting the circumstances of his recruitment, Delroy was a bitter and disruptive presence at first; but he gradually became a valued and enthusiastic Avenger, thanks in part to advice and support from Warbird and Pulsar.
Teaming with Tremont to confront the cosmic menace known as the Triple-Evil, the Avengers learned that Tremont had founded the Triunes to face the Triple-Evil; that he had smeared the Avengers' reputation as part of his efforts to amass Triune influence; that only three scattered cosmic energy shards formed by the universe as "cosmic antibodies" could neutralize the Triple-Evil; and that two of these shards had come to Earth, where one empowered the 3-D Man (a triple-powered 1950s hero formed by the merger of brothers Hal and Chuck Chandler) and another empowered Tremont, who secretly captured 3-D Man in recent times and merged him into unwitting Triune follower Delroy. Having found the third energy shard in space while facing the Triple-Evil, Tremont tried to take all three shards for himself, but Delroy-still merged with the now-conscious Chandlers-absorbed all three shards.
With his newly cosmic power, Triathlon banished the Triple-Evil and helped liberate Earth from Kang; he then gave up his cosmic powers-which had been fuelled by the souls of the Triple-Evil's countless victims-and used the last of his cosmic energy to restore the Chandlers to their separate human forms, regaining his own normal form in the process. Declining to participate in the Triunes' reorganization after Tremont's death in battle with the forces of Kang, Triathlon soon left the Avengers as well, though he has returned to aid them against threats such as Scorpio and an insane Scarlet Witch.