Deiotarus of Galatia (in Galatian and Greek Deiotaros); ca 105 BCE – 42 BCE, 41 BCE or 40 BCE) is a Chief of the Tolistobogii at Western Galatia, Asia Minor, and a King of Galatia (Gallo-Graecia) at Anatolia, Asia Minor.

He is considered one of the most adept of Celtic kings, ruling the three tribes of Celtic Galatia from his fortress in Blucium.

The name Deiotarus is understood as deio-taruos or "divine bull".