The Mega Man series is loaded with Robot Masters. Over the eight main-series games, there have been 64 (including the two from Mega Man Powered Up -- why not), and that doesn't even begin to encompass the enormous crowd of themed robots who jump around in a prescribed pattern and fire some kind of stealable weapon at (a) Mega Man.
What's your favorite? Ours is Wood Man, because he's just impractical enough to be hilarious -- evidently, Dr. Wily knew the whole Robot Master thing was a wash fairly early, but was contractually obligated or something, so he built one on the cheap out of stuff he found behind his house. Why else make a wooden robot to fight a super-powerful enemy? And yet, he still kind of has a sensible theme, unlike, say, Shade Man.