Mind flayers, also called illithids, are the scourge of sentient creatures across countless worlds. They're known as psionic tyrants, slavers, and interdimensional voyagers that harvest entire races for their own twisted ends. They subsist on the brains of humanoids, which provide enzymes, hormones, and psychic energy necessary for their survival. They will sometimes harvest a brain rather than devour it, using it as part of some alien experiment or transforming it into an intellect devourer.
Solitary mind flayers are likely rogues and outcasts. Most illithids belong to a colony of sibling mind flayers devoted to an elder brain-a massive brain-like being that resides in a briny pool near the center of a mind flayer community.