Zoilus I Dicaeus (Ancient Greek: Ζωΐλος Δίκαιος, romanized: Zōïlos Dikaios; epithet means "the Just") was an Indo-Greek king who ruled in Afghanistan and Pakistan and occupied the areas of the Paropamisade and Arachosia previously held by Menander I.

He may have belonged to the dynasty of Euthydemus I. Zoilus used to be dated after the death of Menander, c. 130–120 BCE (Bopearachchi).

Zoilus I uses a silver coin type similar to that of Euthydemus II, son of Demetrius: Crowned Herakles standing, holding a wreath or diadem in his right hand, and a club and the lion skin in his left hand.

In place of his Greek epithet "the just", Zoilus' Indian-standard coins bear the Pali title Dhramikasa ("Follower of the Dharma"), probably related to Buddhism.

His bronze coins are square and original in that they combine the club of Heracles with a Scythian-type bowcase (for a short recurve bow) inside a victory wreath, suggesting contacts or even an alliance with horse-mounted people originating from the steppes, possibly either the Scythians (future Indo-Scythians), or the Yuezhi who had invaded Greco-Bactria.