King Narai the Great (Thai สมเด็จพระนารายณ์มหาราช) (died July 11 1688) became king of the Ayutthaya kingdom or Siam, today's Thailand, in 1655. Under his rule, Siam first opened its borders to western ambassadors and traders.

After king Prasat Thong died, his sons began to fight over the succession. Two kings were crowned and quickly put to death, until stability returned with the coronation of Narai on September 26 1655.

Narai allowed French missionaries to settle in Ayutthaya in 1662, and in 1664 the Dutch enforced a monopoly in fur trading by a sea blockade of Ayutthaya. This even led Narai to build a second capital in Lopburi and site his palace there.

In 1675 the Greek adventurer Constantine Phaulkon came to Ayutthaya and started working for the royal court. In time he became First Counsellor of the king, a position which gained him much envy among the other members of the court. Paired with xenophobic prejudice it made Phaulkon a controversial person - he is still controversial among historians today.

King Narai had no heir, but he wanted his foster son Mom Pi to follow him on the throne, a choice also preferred by Phaulkon. However, when Narai became terminally ill, his old foster brother Petraja started a coup d'état and killed both Mom Pi and Phaulkon, leaving Narai to die with the knowledge that his power has slipped away. Petraja then expelled the French and cut the connections with the west, until King Mongkut reestablished them in the 19th century.