Splinter is a mutant rat in Teenage Mutant Ninja Turtles and Teenage Mutant Ninja Turtles II: The Secret of the Ooze. The pet rat of ninja Hamato Yoshi, Splinter learned many aspects of martial arts as well as Japanese philosophy from his master. After Yoshi is murdered by the Shredder, the rat retreats to the sewers, where he's mutated by a toxic substance or "ooze."
Splinter serves as mentor and father figure to the Ninja Turtles, also mutated by the ooze. He lectures them on the importance of retaining a low profile as well as the discipline and mindset required to be a true ninja. In many ways, his characterization is reminiscent of both Yoda and Pat Morita.
The Splinter puppet was re-designed by Peter Brooke for the second film, with more fur and sharper ears. For the first film, Rob Tygner assisted in operating Splinter, and Sue Dacre did likewise for The Secret of the Ooze. Rickey Boyd assisted on both films.