Diodotus I (flourished 3rd century bc) was the satrap (governor) of the Seleucid province of Bactria, who, with his son of the same name, founded the Greek kingdom of Bactria.
At first subject to the Seleucid king Antiochus I and later to Antiochus II, Diodotus rebelled in about 250 and took the title of king. Little is known of his reign, but, according to some scholars, the Seleucid king Seleucus II, in order to secure Diodotus’ friendship, married one of his sisters to him during a time (246) when the Seleucid Empire was in chaos. Diodotus was succeeded by his son, Diodotus II, and after his death was called by the cult-name Soter (Saviour).