"Try to resist my highly attractive fanged and sphinctered mouth, will you?"
- – Drazlik, the kopru
Kopru are a race of malevolent, mind-controlling aquatic humanoids, which look something like a twisted cross between an illithid and a merfolk. They first appeared in X1: The Isle of Dread in the Mystara setting for Dungeons & Dragons.
They live near undersea volcanoes and thermal vents.
Despite their malign nature, they actually had PC stats for BECMI in PC3: The Sea People from the Creature Catalog series of splatbooks.
They got updated to 3rd edition in Monster Manual II.