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 Humans, shaped similarly to that of Vulcans, except they were smaller and had a more flat point on top. (TOS: "The Corbomite Maneuver")