[Sataninjaku]

Quote:

Originally Posted by jscott991

He's never a full-on rat. In the 1987 show, he is a human in the sewers who takes care of four baby turtles. They are then all mutated by the pink (later green) mutagen, and he becomes a rat/man hybrid.

I can't speak for the "every other iteration" bit, I only followed the original TMNT, but in the '90 film, he is indeed the pet rat- remember the scene in which Splinter tells Danny his origin story? In fact, here it is:

IIRC, this was also the case in the Mirage comics.

But yes, in the original 'toon and toyline, he was indeed Yoshi himself.