Answer
Mongkut's successor was Rama V, also known as King Chulalongkorn. He was the fifth king of the Chakri Dynasty and reigned from 1868 to 1910. Rama V was a progressive monarch who oversaw many reforms in Siam, including the abolition of slavery and the introduction of Western-style education. He also opened Siam to foreign trade and investment, and oversaw the country's transition from a traditional monarchy to a modern state.