… rides a fat horse around.

An old animated film where a good guy is transfigured into a hooded figure who is the hero of the film but no one knows it. He helps out through the whole film and the other characters don’t know who he is until the end. He is transformed to this figure by a wizard or sorceress of sorts and rides around on his stead (which is like the rotund depictions of a horse, similar to the animation within the movie Wizards).  That’s all I can remember at this time. Please help!!! Thank you!