Mr. Perfect is an unknown creature, although his species name could just be "Perfect".
(referring to the song "Torture" from Battle Maximus, the following lyrics:
"In the realm of the Perfects")
He is one of the tallest characters that has been on stage with GWAR, and he is not very well-known. He came from the future to strip GWAR of their immortality, then use it to mutate mankind into his twisted version of what the "perfect" human should be. He is ultimately responsible for "stealing Oderus's immortality and impaling him with his own sword". He was defeated when the band summoned Gor-Gor.
He is shown killing Oderus in a flashback in issue #1 of the 2017 comic Gwar: Orgasmageddon.