Including the brief period of time when it was called “Dark Arts",” there were 7 different professors that taught (Defense Against) the Dark Arts at Hogwarts:
Quirinius Quirrell
Gilderoy Lockhart
Remus Lupin
Alastor Moody/Bartemius Crouch, Jr.
Dolores Umbridge
Severus Snape
Amycus Carrow (he taught as Dark Arts)