I'm trying to figure out why Calvin is even used, and all I can get is the lame almost-ryhme in the title. Calvin could be anyone or no one, all the character does is stand there and say "What's the punchline, Mr. Jobs?"
(Hell, Hobbes minus Calvin would be trippy enough, since Hobbes is the imaginary friend...)
The portion of Hobbes that is real is just an inanimate stuffed toy tiger. Hobbes as a motile, living, thinking being exists entirely as a figment in Calvin's mind, projected into the object of the toy tiger. So Hobbes the toy is real, while Hobbes the being is imaginary.