Demogorgon
Demogorgon is the most famous, or at least infamous, Demon Prince in Dungeons & Dragons. Having been around in every single edition since the game was created, he is the Prince of Demons - the closest thing the Abyss has to a singular, all-powerful ruler, with only Orcus and Graz'zt really having any chance of challenging his might.
Demogorgon is infamous for taking the somewhat mix'n'match appearance of early D&D demons and really turning it to his advantage. For the most part, Demogorgon resembles something almost dinosaurian; a giant, bipedal, predatory reptile. Except he's got two heads, resembling the heads of baboons (or mandrils, but they're close enough), and each arm splits into two tentacles.
Perhaps the greatest limitation that Demogorgon faces is that he is legitimately insane; each head has its own unique personality, and so he's constantly fighting himself to determine which persona gets to be top dog.