Jack Kirby did several illustrations of the Teenage Mutant Ninja Turtles on behalf of his friend, Kevin Eastman. He supposedly liked the idea and thought it had great potential.
It was pretty easy to get sketches from Jack at the end. In the years before he died, Jack Kirby was not well liked in the comics world. He was rather like Michael Jackson in that he became a near demigod after death, after a decade or so of being taken for granted.