Balok's species were a humanoid race from the Alpha or Beta Quadrant and members of the First Federation. In their initial appearance to the crew of the USS Enterprise, Balok, a member of this species, appeared to be a bluish, cat-eyed alien. In his true form, he resembled a Human child.
Members of Balok's species were small, about the height of a Human child, and usually bald, with hair mainly on their eyebrows. Their ears were different from other humanoids, shaped similarly to that of Vulcans, except they were not as pointed and were slightly smaller. (TOS: "The Corbomite Maneuver")