I've been granted access to the Teeth of Naros by a strange entity that claims it brought me here. I'm supposed to "seek the Primos." I should see if there's some way for me to find out what this means.
The easiest way to kill him is to take out the two Kobolds behind him, which will lower his damage resistance and prevent him from regenerating health. On the PC version, after killing both Kobolds they can clone one at a time.
However, killing him while leaving the Kobolds alive earns the achievement "The Harder They Fall.