The Bi-Beast was originally a huge android with two heads (one atop the other - the top skull is given knowledge of warfare while the bottom skull was given a knowledge of culture) created many years ago by an Avian race that were in turn a sub-species of the Inhumans. For reasons unknown, the Avian race dies out, and the Bi-Beast is left to its own devices in the Avian city. Years later, the creature sees the Harpy with Bruce Banner, and is reminded of its former Avian masters. The Bi-Beast captures them both and instructs Banner to fix the now-decaying machines in the city. Banner instead chooses to cure the Harpy, who reverts back to her original form of Betty Ross soon after. The Bi-Beast becomes aware of Banner's deception and fights Banner's alter-ego the Hulk, but is distracted when an AIM strike force led by Modok storms the city. Rather than allow its home to be captured, the Bi-Beast activates a self-destruct mechanism and perishes in the explosion. 
Unknown to all, a cylinder containing a second Bi-Beast is ejected from the city at the moment of the explosion. It comes to rest on the ocean floor, and is later retrieved and taken to the SHIELD helicarrier. The second Bi-Beast awakens soon after, and imbued with the memories of the first, decides to take control of the helicarrier and launch its missiles at major metropolitan cities, believing the human race to be responsible for the extinction of the Avian people. General Thunderbolt Ross becomes aware of the danger and forcibly inserts Bruce Banner into the helicarrier, where he changes into the Hulk and battles the Bi-Beast once more. The two fall mid-battle through an opening activated by SHIELD, and plunge many miles to the ocean. The Bi-Beast disappears and is assumed to have drowned. 
Several years later the Bi-Beast reappears. The android captures and enslaves the crews of naval ships and slowly builds an army for another revenge attack on the human race. Donald Blake, however, is traveling on the latest vessel to be attacked (planted there by Tony Stark - the alter ego of Iron Man - who was aware of Blake's true identity and wanted some added "insurance") and becomes Thor, who quickly defeats the Bi-Beast and frees the captives. An apprehended Bi-Beast is then freed by his secret ally, the Man Beast, and together the two battle Thor and Iron Man. 
Defeated once more, the Bi-Beast is eventually captured by the Stranger for study.  He later battles the Hulk and ally She-Hulk. Bi-Beast's effectiveness is compromised when one of his heads develops an attraction to She-Hulk.
The Bi-Beast was seen battling the Thing and Squirrel Girl, and as a corpse in the series Beyond!, although it is unclear as to whether the latter is, in fact, canon.