The ape-like, acrobatic mutant adventurer and brilliant biochemist known as the Beast applied to join during an Avengers membership drive and was accepted as a probationary member. 

     He soon became a full member and served a lengthy tour of duty before resigning to reserve status during a membership reshuffling. 

     He later became a core member of the Defenders, and after their disbanding he helped found the new mutant team X-Factor. 

     More recently, he rejoined the X-Men, a team of mutant adventurers he had helped found years earlier. 
  

     He has also sustained a friendship with longtime Avengers member Wonder Man, and with fellow X-Men such as Archangel, Iceman and Dazzler.

     Mutating further in recent times, Beast has taken on a less human, more animalistic and vaguely feline appearance.