Aboleth

Aboleths are eel-like amphibians of immense size with long, tubular bodies, lamprey-like mouths filled with serrated, jawless teeth, and massive god complexes. They are virtually immortal and will not die of old age, and they will continue to grow as they age with the average specimen measuring 20 feet in length and weighing 6,500 pounds, though some ancient beings are much larger.
Aboleths hail from the Far Realm, a place of dreams and nightmares beyond this plane's comprehension, and like other denizens of that wretched place, they have powerful psionic powers and are natural psions.