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behold the first king of the Abyss in all his strangeness. Note that the three skulls are actually on his tail

Obox-ob is Prince of Vermin, an ancient obyrith demon; he rules layer 663 of the Abyss. He is allegedly the last surviving aspect of the old Prince of (all) Demons. He hates the tanar'ri and wants to ethnically cleanse the Abyss from them, as well as overthrow Demogorgon.

The Demon Princes of Dungeons & Dragons
Tanar'ri: Baphomet - Demogorgon - Doresain - Fraz-Urb'luu - Graz'zt
Juiblex - Kostchtchie - Lolth - Malcanthet - Miska the Wolf-Spider
Orcus - Sess'innek - Shaktari - Turaglas - Yeenoghu - Zuggtmoy
Obyrith: Dagon - Obox-ob - Pale Night - Pazuzu - The Queen of Chaos - Sertrous