Herman series
The Herman series was a group of androids who inhabited the planet Mudd. 

Like most, if not all, of the "masculine" models of Mudd androids, the Herman series pre-dated the accidental arrival of fugitive Harry Mudd. ()

Background information 
The Herman series, only identified in dialogue, were established by the Star Trek Concordance to be the series portrayed by uncredited twin brothers Tom and Ted LeGarde, as well as Billy Blackburn. 

According to Blackburn, "In "I, Mudd", there was two sets of twins. Two girls and two guys. And when the guys came in they looked so much like me that they decided to put me in the same costume as they were in so that it would be even three androids rather than two male androids. So it was quite a shock because we really did look alike and we were the same height and same build. I had tight, and, like off-white, gray tights and a matching – long-sleeved, matching top. And not stiff makeup but makeup that was really thick to make you look more like a... We were supposed to be dolls, in fact. That's what we really were." (Billy Blackburn's Treasure Chest: Rare Home Movies and Special Memories, Part 2)

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Androids