Gold coin of Diodotus c. 245 BC
Diodotus I Soter (Greek: Διόδοτος Α’ ὁ Σωτήρ) (c. 285 BC – c. 239 BC) was Seleucid satrap of Bactria, rebelled against Seleucid rule soon after the death of Antiochus II in c. 255 or 246 BC, and wrested independence for his territory. He died in 239 BC.

This event is recorded by Trogus, Prol. 41; Justin xli. 4, 5, where he is called Theodotus; Strabo xi. 515). The name apparently is related to the title Soter he uses for himself. His power seems to have extended over the neighbouring provinces. Diodotus was a contemporary, a neighbour, and probably an ally of Andragoras, the satrap of Parthia, who at about the same time also proclaimed independence from the Seleucid Empire.