Thomas Clement Douglas PC CC SOM (20 October 1904 – 24 February 1986) was a Scottish-born Canadian politician who served as the seventh premier of Saskatchewan from 1944 to 1961 and leader of the New Democratic Party from 1961 to 1971. A Baptist minister, he was elected to the House of Commons of Canada in 1935 as a member of the Co-operative Commonwealth Federation (CCF). He left federal politics to become leader of the Saskatchewan Co-operative Commonwealth Federation and then the seventh Premier of Saskatchewan. His government introduced the continent's first single-payer, universal health care program.

After setting up Saskatchewan's universal healthcare program, Douglas stepped down and ran to lead the newly formed federal New Democratic Party (NDP), the successor party of the national CCF. He was elected as its first federal leader in 1961. Although Douglas never led the party to government, through much of his tenure the party held the balance of power in the House of Commons. He was noted as being the main opposition to the imposition of the War Measures Act during the 1970 October Crisis. He resigned as leader the next year but remained as a Member of Parliament until 1979.

Douglas was awarded many honorary degrees, and a foundation was named for him and his political mentor M. J. Coldwell in 1971. In 1981, he was invested into the Order of Canada, and he became a member of Canada's privy council in 1984, two years before his death. In 2004, a CBC Television program named Tommy Douglas "The Greatest Canadian", based on a Canada-wide, viewer-supported survey.

Thomas Clement Douglas was born in 1904 in Falkirk, the son of Annie (née Clement) and Thomas Douglas, an iron moulder who fought in the Boer War. In 1910 at age 7, his family immigrated to Canada, where they settled in Winnipeg. Shortly before he left the United Kingdom, Douglas fell and injured his right knee. Osteomyelitis set in and he underwent a number of operations in Scotland in an attempt to cure the condition. Later in Winnipeg, the osteomyelitis flared up again, and Douglas was sent to hospital. Doctors there told his parents his leg would have to be amputated; however, a well-known orthopedic surgeon took interest and agreed to treat him for free if his parents allowed medical students to observe. After several operations, Douglas's leg was saved. This experience convinced him that health care should be free to all. Many years later, Douglas told an interviewer, "I felt that no boy should have to depend either for his leg or his life upon the ability of his parents to raise enough money to bring a first-class surgeon to his bedside."

During World War I (aged 12 to 15), the family went back to Glasgow. They returned to Winnipeg in late 1918, in time for Douglas to witness the Winnipeg general strike. From a rooftop vantage point on Main Street, he witnessed the police charging the strikers with clubs and guns, and a streetcar being overturned and set on fire. He also witnessed the Royal Canadian Mounted Police (RCMP) shoot and kill one of the workers. This incident influenced Douglas later in life by cementing his commitment to protect fundamental freedoms in a Bill of Rights when he was premier of Saskatchewan.

In 1920, at the age of 15, Douglas began amateur boxing at the One Big Union gym in Winnipeg. Weighing 135 pounds (61 kg), he won the 1922 Lightweight Championship of Manitoba after a six-round fight. Douglas sustained a broken nose, a loss of some teeth, and a strained hand and thumb. He held the title the following year.

In 1930, Douglas married Irma Dempsey, a music student at Brandon College. They had one daughter, actress Shirley Douglas, and they later adopted a second daughter, Joan, who became a nurse. His daughter, Shirley, married actor Donald Sutherland; through Shirley, Kiefer Sutherland is Tommy Douglas’ grandson.

Douglas started elementary school in Winnipeg. He completed his elementary education after returning to Glasgow. He worked as a soap boy in a barber shop, rubbing lather into tough whiskers, then dropped out of high school at 13 after landing a job in a cork factory. The owner offered to pay Douglas's way through night school so that he could learn Portuguese and Spanish, languages that would enable him to become a cork buyer. However, the family returned to Winnipeg when the war ended and Douglas entered the printing trades. He served a five-year apprenticeship and worked as a Linotype operator finally acquiring his journeyman's papers, but decided to return to school to pursue his ambition to become an ordained minister.