Mugato

The Mugato were a simian-like creature that inhabited some regions on the planet Neural.

They are large and intimidating creatures that reach up to 2 metres tall and are covered by a coat of thick white fur, except for their hands and face, and large thick horns that protrude from the top of their heads, and smaller horns that stretch down their backs. They also have strong teeth and fangs, which contain a venom that can be lethal to many creatures, including Humans. (TOS episode: "A Private Little War").

A common insult used in the 23rd century, was that Klingons didn't have the brainstem of a mugato. (TOS comic: The Ashes of Eden).