Eucratides I Megas (reigned c. 171–145 BCE) is one of the most important Greco-Bactrian kings, who are descendants of dignitaries of Alexander the Great.

He uproots the Euthydemid dynasty of Greco-Bactrian kings and replaces it with his own lineage.

He fights against the Indo-Greek kings, the easternmost Hellenistic rulers in northwestern India, temporarily holding territory as far as the Indus, until he is finally defeated and pushed back to Bactria.

Eucratides has a vast and prestigious coinage, suggesting a rule of considerable importance.