These fishlike beings of the Underdark and the deeps inspire terror with their alien appearance and psyche. The cold, unblinking stare of their bulbous eyes and the horrific reek of decayed sea life that always hovers around them bring a chill to the spine of the most stalwart warrior. What goes on inside the inhuman minds of these cold-blooded creatures defies contemplation, and what ancient horrors they consort with in the deepest chasms of the world are better left unknown.
In a monstrous campaign, I once played a Kuo-Toa monk that left his cavern to break free from the insanity that plagued his race. Vorrip was one of the funnest characters I have played. It was neat to really role play his alien nature.
The Kuo-Toa appears in the latest version of the D&D Monster Manual:
Dungeons & Dragons Monster Manual - 4th Edition