Visser Three is a recurring enemy of the Copy Crisis. A bizarre alien entity, Visser Three is hard to describe, though he basically looks like a blue centaur with no mouth, a scorpion tail and two eyestalks atop his head. He oversaw the invasion of Earth by a strange slug-like species of aliens called Yeerks with plans to destroy the Andalite race and conquer the galaxy.
He first appeared in the epilogue "Rock 'n' Rolled" at what first seemed to be a Rush conert the Copies were attending, eventually revealing that it was all a set-up in order to destroy them, as he mistakenly believed they were Andalites. Despite his group of Hork Bajir minions, Visser Three was defeated and knocked back from whence he came.
He later re-appeared in "The Appliance of Science", in which he posed as a judge at a science fair Marl was attending, once again revealing to have simply lured him into a trap. He and his minions were defeated once again, though the villainous Visser had managed to steal Marl's molecular rearranger, which he presented to his "master". Chances are, the crazy centaur-thing isn't done yet....