Fonzie's rough past earns him a great deal of respect and fear from more antagonistic characters. Throughout the series he served as defender and protector of Richie, Ralph, and Potsie whenever they were confronted by various bullies and hoodlums. Various episodes indicate that Fonzie has extensive martial arts training. Even opponents larger than he are shown to back down from confrontations. Those who do fight him never come out on top. In one episode, he compares his nerve strike knowledge to that of a woman (Katmandu) while both use Ralph as a training dummy. In subsequent episodes, he out-dueled an expert fencer and mangled a gangster's prosthetic iron hand with one fist. Meanwhile, more sympathetic characters idolize Fonzie due to his success with women and his imperturbable "cool." Despite the respect he has earned, several people still antagonized him – including Officer Kirk (Ed Peck), an overzealous police officer who sometimes (though never successfully) tried to frame Fonzie or run him out of town.