Solomon West Ridgeway Dias Bandaranaike (1899–1959) was Prime Minister of Ceylon from 1956 until his assassination in 1959. He was the son of Sir Solomon Dias Bandaranaike, the Maha Mudaliyar.
Educated at Christ Church, Oxford, he returned to Ceylon, converted from Anglicanism to Buddhism, and founded the Sinhala Maha Sabha in 1937. He left the United National Party in 1951 to form the Sri Lanka Freedom Party, and won the 1956 election at the head of a coalition that mobilised Sinhala Buddhist opinion, particularly among rural teachers, monks, ayurvedic physicians and village officials.
His government passed the Sinhala Only Act of 1956, making Sinhala the sole official language. It is the most consequential legislation of the post-independence period: it responded to a genuine grievance about the dominance of English among a small elite, and it simultaneously excluded Tamil speakers from public life in a way that shaped the conflict of the following decades. He was shot in September 1959 by Talduwe Somarama, a Buddhist monk, and died the next day.