Splinter

Splinter, often referred to as Master Splinter or Sensei by his students/sons, is a fictional character from the Teenage Mutant Ninja Turtles comics and all related media. A mutant rat, he is the grave and stoic sage of the Turtles, their ninjutsu and martial arts instructor, and their adoptive father. Originally depicted as the pet rat of martial artist Hamato Yoshi (Japanese: 濱戸義), in later works he is sometimes portrayed as Yoshi himself, mutated or reincarnated. The character was originally a parody of the Marvel Comics character Stick.