Well, I'm an idiot. I stupidly neglected to mention William O. Douglas Jr. in my spotlight of "The Galaxy Being" last month. He was the man inside the Andromedan costume, the inaugural Outer Limits "bear," so he was certainly more than deserving. However, his importance to the TOL universe is much broader than that: he appeared in a total of four episodes, and inhabited three different alien/monster get-ups (his fourth appearance was actually a human character; however, he did wind up getting hunchbacked, so there's that). To atone for my egregious omission, I've prepared a special spotlight of his work on the show.
Andy the Andromedan ("The Galaxy Being")
The Ghost of Private Gordon/The Ice Ghost ("The Human Factor")
Henry Castle ("The Invisibles")
Aabel of Eros ("The Children of Spider County")