Keaton is a character in Creatures of the Void who starts as a misguided antagonist and later enters the heroes' team.
He has been hunting the Omnibrine for an unspecified (but long) amount of time, though he does not realize prior to the story that the Creation of the Void he is hunting is the same being as the prophesied Omnibrine. He has resorted to attempting to kill it via any way possible, including attempting to kill Steve in order to prevent it from forming.
In the season finale, he accidentally causes the Omnibrine to form into several different fragmented pieces using a Motion Arrow.
Keaton hunts Steve for most of season one in order to preemptively kill the Omnibrine before it can form. This results in the near-destruction of Alex's tube cave, as well as both Jennifer and Samuel being killed impermanently, setting up the plot of most of Secret of the Daydream. At the conclusion of season one, Steve forgives Keaton and resolves to work together to kill the Omnibrine.
Alex in concept is indifferent to Keaton's existence and him to hers, but in practice, they end up enemies due to his siege of her cave, though they don't directly fight.
Keaton's primary goal is the killing of the Omnibrine, which leads him into contact with the players. The Omnibrine lost many of its weaknesses as soon as it became complete with all eight players, leading Keaton to try to kill Steve in order to undo this.
In the season finale, he accidentally fires a Motion Arrow at the Omnibrine instead of a regular arrow, which reacts with the Worldbolt by disseminating its current held energy instead of causing it to explode. This forms Herobrine, Herabrine, Blackthorn, etc. but is ultimately instrumental in freeing Steve from Muriminus' chains.
Keaton joins the team, as Steve is able to see through his anger and realize that they only had the same goal: to kill the Omnibrine. He is originally held under suspicion of perma-killing Jennifer and Samuel, but reveals that he did not use his Deconstruct Sword on them, as they were not his enemy and did not need to perma-die (giving him traits of an Anti-Villain). He helps the team search for and find Samuel.
Steve: Team member
Alex: Team member