Bullhorn began as a human from Mexico, a petty thug and street fighter surviving on his brawling earnings. His life shifted dramatically when the Decepticons, influenced by Devil Z, recruited him with a more lucrative offer. He joined primarily for financial gain, viewing his role as a transactional business arrangement rather than embracing their ideology, and explicitly voiced concern about preserving Earth as a viable base for future operations.

As a Decepticon Headmaster Junior, Bullhorn bonded with a mechanical transtector from the planet Master, which transformed into a monstrous buffalo. This body featured specialized capabilities like infrared scopes for night combat and temporary chameleon-like camouflage. Bullhorn operated closely with fellow Headmasters Wilder, an American biker gang leader, and Cancer, a Chinese orphan martial artist, forming a tight-knit trio. He demonstrated genuine loyalty to them, considering them true friends and often protecting their well-being in battle.

Bullhorn participated in numerous Decepticon missions: causing urban chaos to lure Autobots, attempting to reform Wilder's gang, searching globally for Godmaster candidates, kidnapping children as bait, destroying food supplies, and assaulting Autobot positions. He frequently showed impatience with assignments he deemed tedious, like reconnaissance or stakeouts, preferring direct action. His commitment wavered as Devil Z's plans escalated towards human extinction, creating moral unease. This culminated upon witnessing the betrayal of Decepticon Godmaster Doubleclouder and hearing Cancer express doubts. When Cancer defected to aid Autobot Ginrai against the Seacons, Bullhorn intervened, destroying the Seacons targeting Cancer and urging him to escape.

Following this, Bullhorn and Wilder rejected both the Decepticons and Devil Z but declined formal Autobot membership. They briefly departed before unexpectedly returning to assist Cancer and the Autobot Juniors in a perilous battle, prioritizing their bond with Cancer over faction loyalty. In the final Grand Canyon confrontation against the merged Devil Z and BlackZarak, Bullhorn fought alongside the Autobots. A blast of Devil Power separated him and the other human partners from their transtectors, simultaneously animating the transtectors into independent robotic lifeforms. Bullhorn's sentient transtector, inheriting aspects of his personality, joined the other Decepticon transtectors departing Earth to continue the war in space under Overlord's command in the G Nebula.