Diodotus I Soter (Greek: Διόδοτος Σωτήρ), also known as Diodo (c. 285 BC – c. 235 BC) was the first Hellenistic king of Bactria. Diodotus became independent of the Seleucid empire around 255, and established the Diodotid Kingdom, which endured in various forms until the beginning of the first century AD. In 245 Diodotus repelled a Parthian invasion of Bactria by Arsaces, but little is known about this war. He also minted an extensive coinage and administered a powerful and prosperous new kingdom. He died around 235 BC of unknown causes and was succeeded by his son, Diodotus II.