The Teenage Mutant Ninja Turtles (or simply Ninja Turtles, and previously known in the United Kingdom, Germany, Austria, Ireland and Scandinavia as Teenage Mutant Hero Turtles) are a fictional team of four mutant turtles, who are trained by their sensei, Master Splinter, in the art of Ninjutsu. From their home in the storm sewers of New York City, they battle petty criminals, evil megalomaniacs, and alien invaders, all while remaining isolated from society at large.