Several years ago, a team of scientists conducted atomic tests in the deserts of Arizona. On the surface, the tests met with optimal success, but the seismic vibrations cracked open a fault line, creating a trench that stretched northward into a glacial cavern in Canada. Inside the frozen ice was the slumbering form of a creature of myth: a sub-human man-ape that the Japanese referred to as a Yetrigar. Nuclear radiation from the Arizona desert traveled through the geological pipeline, awakening the creature.
This Yetrigar instinctively began traveling southward, following the trail of radiation to its origin point. Over the course of three months, the radiation had a profound physiological effect on the plodding creature. With each passing day, he grew bigger and bigger until finally his immense size dwarfed even the surrounding trees.
Yetrigar's journey terminated at the Grand Canyon where he encountered a S.H.I.E.L.D. Helicarrier in pursuit of the mutated dinosaur known as Godzilla. Acting out of some primal fury, Yetrigar hurled a boulder at the ship, downing the Behemoth class Helicarrier. All personnel aboard the Helicarrier survived the crash and young Robert Takiguchi, recognizing the threat that the Yetrigar represented, took it upon himself to pilot the Red Ronin armor in the hopes of stopping him. 
Within moments of this incident, Godzilla appeared on the scene and engaged in battle with Yetrigar. The two grappled with one another atop one of the numerous buttes in the canyon and Yetrigar proved to be invulnerable to most of Godzilla's attacks, including his powerful atomic breath. The two beasts collided with one another, toppling down into the canyon below. Red Ronin attempted to separate the two, acting mostly out of defense of Godzilla. Yetrigar tackled Red Ronin, but the giant robot armor kept him at bay with his electro-sword. He even succeeded in executing the "sleeper hold" on Yetrigar, but the beast broke the grip and continued fighting against Red Ronin and Godzilla. Takiguchi realized that the Yetrigar was too powerful to stop through conventional means, so he fired his rockets at the cliff's edge that caused a rock slide, burying Yetrigar beneath a ton of dirt, rocks and debris. Yetrigar remained buried in the Grand Canyon for several years. S.H.I.E.L.D. kept a file on him, but never made any efforts to recover the creature.
A few short years later, a former S.H.I.E.L.D. agent named Bobbi Morse, aka Mockingbird, suggested to her teammates in the West Coast Avengers that they should take a vacation in the Grand Canyon. Bobbi knew from reading S.H.I.E.L.D. reports that the Yetrigar was buried here. She had private matters to attend to in this region, and decided to awaken the Yetrigar to keep her teammates distracted while she pursued her own agenda.
While the West Coast Avengers were exploring the cavern, Mockingbird tossed an explosive into the valley where she knew the Yetrigar lied buried. The explosion awakened the creature, and he began terrorizing the valley. Of all the Avengers present, only Wonder Man possessed enough power to stun the rampaging creature. Yetrigar began thrashing, smashing at the cliffs' edge, endangering the lives of several tourists. Hank Pym and Tigra scaled the side of Yetrigar's hairy hide until they reached his ear. Pym inserted an electrical device inside of the monster's ear, then used his Pym Particles to enlarge it. The device caused Yetrigar intense physical pain, ultimately rendering him unconscious. 
Powers and Abilities
Even at his original size, Yetrigar's physical attributes were likely several times greater than a normal human being. After being affected by nuclear radiation, his physical attributes increased exponentially.
- The general populace of Earth is largely unaware of Yetrigar's existence and believes him to be a creature of myth.