A huge, primitive-looking thrall kept as a fighter by the Providers of Triskelion, who is set against a bound Captain Kirk in 2268 as a punishment and a test.
Kloog appears in the second-season episode The Gamesters of Triskelion. He is one of the thralls trained by Galt for the combats on which the Providers wager, alongside Shahna, Lars and Tamoon.
When Kirk steps in to take a punishment meant for Uhura, he is tied by the wrists and put in the arena against Kloog, who is armed with a whip and a net. Shahna warns him that Kloog's left eye is weak. Kirk uses the advantage and manages to get his bonds around Kloog's throat before Galt stops the bout, and the Providers begin bidding for the newcomers.
Kloog fights again in the final contest, when Kirk stakes his crew's freedom on beating three thralls at once. He was played by Mickey Morton.