It is similar to regular mole rats, but much smarter and capable of speech. It can be found deep underground in the rat infested caves beneath Klamath and seems to be able to control an army of smaller mutant rodents.
He has a brother - Brain, who is less aggressive towards humans. If you kill Keeng Ra'at his brother will comment on it when you meet him, but he won't be aggressive.
Due to its high HP and AP, Keeng Ra'at can be particularly difficult for a low-level character. If you have acquired some kind of firearm (most likely to be a pipe rifle or a 10mm pistol - if you haven't found a 10mm pistol, there is one conveniently located on a corpse just above the room where Keeng Ra'at resides) and have a good small arms skill, a relatively easy way to kill Keeng Ra'at this early is to shoot him in the hind legs until at least one of them are crippled. This will severely hamper his movement speed, so you will be able to easily outmaneuver him and shoot. Acquiring Sulik early on and bringing him along for the fight should make it easier for a low-level player.