Hobbes(left) and Tiger Calvin(right) make first contact.
Tiger Calvin appears in a single story arc; after having invented the Transmogrifier, Calvin asks for Hobbes' assistance to be turned into a tiger. Over the course of the story arc Calvin realizes that being a tiger isn't as fulfilling as he had imagined, and turns himself back into a human boy. Tiger Calvin is never seen or mentioned again, although a year later Calvin (unsuccessfully) attempts to assimilate the lifestyle of a tiger.