Mongkut[a] (18 October 1804 – 1 October 1868), posthumously honoured as King Mongkut the Great, was the fourth king of Siam from the Chakri dynasty, titled Rama IV.[2] He reigned from 1851 until his death in 1868. The reign of Mongkut was marked by significant modernization initiatives and diplomatic engagements, which played pivotal roles in shaping Siam's trajectory towards progress and international relations. It was during his reign that Siam first felt the pressure of Western expansionism. Mongkut embraced Western innovations and initiated reforms in technology, science, and culture, earning him the posthumous title "the Father of Science and Technology" in Siam. His accurate prediction of the total solar eclipse of 18 August 1868 — later dubbed "the King of Siam's eclipse" — demonstrated his scientific acumen and became a symbol of Siam's engagement with modern science. Mongkut was also known for appointing his younger brother, Prince Chutamani, as Second King, crowned in 1851 as King Pinklao. Mongkut told the country that Pinklao should be respected with equal honor to himself (as King Naresuan had done with his brother Ekathotsarot in 1583). During Mongkut's reign, the power of the House of Bunnag reached its zenith: It became the most powerful noble family of Siam. Mongkut is known in the West primarily through the lens of the 1951 musical The King and I and its 1956 film adaptation, in which he was portrayed by Yul Brynner. Brynner's performance as King Mongkut earned him the Academy Award for Best Actor at the 29th Academy Awards in 1957.