I don't have any of Ken Anderson's sketches depicting this character from Robin Hood, but there is no doubt that Milt Kahl's final design is based on Ken's.
The crocodile's role in the film is very limited, he announces the archery tournament and is a little involved in the fight that follows. Most scenes were animated by Art Stevens.
The character's voice is provided by Candy Candido, a Disney veteran, who had lent his talents to the Indian Chief in Peter Pan.
Milt is so great with alligators and crocodiles. I think his Nero and Brutus from The Rescuers are amazing, and he even had his hand in designing the crocodile in Peter Pan.