* Ruk was played by Ted Cassidy, who at this point is better known from his earlier role as Lurch on The Adams Family. Cassidy would go on to appear in two other episodes of Star Trek, and in one of them he played yet another of the original series' many memorable villains, Gorn.
Or, more properly, Gorn!!!!!
Oh, it's also worth noting that the episode featuring Ruk, "What Are Little Girls Made Of?", was written by Robert Bloch.