Deino, also known as the Fanged Flattooth and the Terror of the Mysterious Beyond, is the main antagonist of the Greatest Adventure trilogy. He is the Land Before Time's most evil villain, even surpassing Sharptooth himself.

His crimes include causing the death of Littlefoot's mother (Arianna), the leader of Tippy's herd, and Ali's great-great aunt Clarice (the Old One), a crime he framed Chomper for, among others.

He has many accomplices, including Sharptooth, Red Claw, Screech, Thud, Rinkus Sierra, Ozzy, Strut, Odul, Ela, Finley, Liz, and the Domeheads.

His Nemesis is Littlefoot with Chomper as a close second.  Deino hates all dinos minus Bothteeth.