Step 1: Identify Megasthenes:
Megasthenes was a Greek ambassador sent by the Seleucid ruler Seleucus I Nicator to the Mauryan court.
Step 2: Identify the Mauryan ruler:
He resided at the court of Chandragupta Maurya (founder of the Mauryan Empire, c. 322-298 BCE) and wrote the account 'Indica' describing the empire.
Final Answer:
\[ \boxed{\text{Chandragupta Maurya}} \]