Being a franchise based on martial arts (although sometimes rather tenuously), sensei are plentiful in Teenage Mutant Ninja Turtles. The most well-known, obviously, is the Ninja Turtles' sensei, Splinter.
In addition to being an honorific term of address, "-sensei" is also a naming suffix that replaces the usual address suffix "-san" in this context. For example, in Japanese, "Splinter-san" addresses Splinter as an ordinary person, while "Splinter-sensei" is the equivalent of "Master Splinter." It is rare in TMNT stories for characters to address sensei characters in a suffixed manner like this, but more common in Usagi Yojimbo stories including TMNT crossover stories. In these stories, Splinter's counterpart Kakera is not addressed as "Master Kakera," but as "Kakera-sensei."