Megasthenes, who wrote the Indica, was an ambassador of Seleucus Nicator at the court of which ruler?

Seleucus Nicator, after his conflict with Chandragupta Maurya around 305 BC, sent Megasthenes to Pataliputra. His Indica, now surviving only in fragments quoted by later Greek writers, describes Mauryan administration and society. Ashoka and Bindusara ruled later, and Harshavardhana belongs to the seventh century AD, long after Seleucus.