Origin

Little is known about the man before Madame Monstrosity combined his DNA with a dog and created Mr. Muttman.

It is Mr. Muttman who makes Boy-Spider costume, but because he is color blind he gets the colors reversed.

Like the rest of the Humanimals, Mr. Muttman turns on Madame Monstrosity when he learns she can't change him back to being a human and she was lying to all the Humanimals.

When Spider-Man and the other smart Humanimals uses their inteligence to turn all the Humanimals back to their orignal forms, it is assumed that Mr. Muttman was changed back too.

Creation

Mr. Muttman was created by Dan Slott and Paco Medina for their series, Spider-Boy. He first appeared in the back-up story Missing Pieces.