Solomon West Ridgeway Dias Bandaranaike (Sinhala: සොලොමන් වෙස්ට් රිජ්වේ ඩයස් බණ්ඩාරනායක; Tamil: சாலமன் வெஸ்ட் ரிட்ஜ்வே டயஸ் பண்டாரநாயக்கா; 8 January 1899 – 26 September 1959), often referred to by his initials as S. W. R. D. or S. W. R. D. Bandaranaike and known by the Sri Lankan people as "The Silver Bell of Asia" (ආසියාවේ රිදී සීනුව), was the fourth Prime Minister of the Dominion of Ceylon (now Sri Lanka), serving from 1956 until his assassination in 1959. The founder of the left-wing and Sinhalese nationalist Sri Lanka Freedom Party, his tenure saw the country's first left-wing reforms.

Born to a wealthy, political family, he studied philosophy, politics, and economics at Christ Church, Oxford, and was called to the bar at the Inner Temple. Returning to Ceylon, he entered local politics by joining the Ceylon National Congress. Having been elected to the Colombo Municipal Council in 1926, he was elected from his family seat in Veyangoda to the State Council of Ceylon for two terms between 1931 and 1947, while serving in the second term as Minister of Local Administration in the Board of Ministers. Having founded the Sinhala Maha Sabha in 1936 on Sinhalese nationalist lines advocating for self-rule in Ceylon, he joined D. S. Senanayake by dissolving the Sinhala Maha Sabha and merging it with the United National Party at its formation in 1947. He was elected to the House of Representatives in 1947 representing the United National Party from Attanagalla, which would become the political seat of his family for the next fifty years. Since the Sinhala Maha Sabha formed the largest segment of the United National Party, D. S. Senanayake appointed Bandaranaike as Minister of Health and Local Government and he was elected as the Leader of the House. Following several disagreements, Bandaranaike resigned from the government and crossed the floor to the opposition, forming the Sri Lanka Freedom Party in 1951. Following D. S. Senanayake's sudden death and the elections that followed, Bandaranaike was elected leader of the opposition. Mustering a powerful coalition called the Mahajana Eksath Peramuna and contesting on the lines of Sinhalese nationalism and socialism, he was able to achieve a landslide victory over the United National Party in the general elections in 1956 thereby becoming the fourth Prime Minister of Ceylon. His tenure saw some of the first left wing reforms instituted by the Freedom Party in Sri Lanka such as the nationalizing bus services and introducing legislation to prohibit caste based discrimination. Bandaranaike removing British naval and air bases in Ceylon and established diplomatic missions with a number of communist states. He implemented a new language policy, the Sinhala Only Act, making Sinhala the sole official language of the country creating much controversy.

On 25 September 1959, Bandaranaike was shot at his town house in Colombo and died of his wounds the day after. A Buddhist monk named Ven Talduwe Somarama was arrested, convicted and hanged for the murder of Bandaranaike. Minister of Education and the acting leader of the house, Wijeyananda Dahanayake was appointed caretaker prime minister by the Governor General and was confirmed by Parliament. Bandaranaike's death led to political turmoil with the Mahajana Eksath Peramuna falling apart under Dahanayake who eventually formed his own party to contest the general elections in March 1960. Although the Freedom Party failed to form a government under the leadership of C. P. de Silva, fresh elections were held four months later after the United National Party government lost the throne speech. Bandaranaike's widow Sirima Ratwatte Dias Bandaranaike lead the Freedom Party to gain a majority in parliament and was appointed the first female Prime Minister in the world. She expanded on her husbands left wing reforms in her two terms as Prime Minister from 1960 to 1964 and from 1970 to 1977. In 1994, Bandaranaike's daughter Chandrika Kumaratunga headed a coalition led by the Freedom Party to be elected Prime Minister and thereafter President serving from 1994 to 2005, during which Bandaranaike's widow served as Prime Minister from 1994 to 2000 and Bandaranaike's son Anura Bandaranaike served as Speaker of the Parliament of Sri Lanka from 2000 to 2001.