Sir John Alexander Macdonald (January 10 or 11, 1815 – June 6, 1891) was the first prime minister of Canada, serving from 1867 to 1873 and from 1878 to 1891. The dominant figure of Canadian Confederation, he had a political career that spanned almost half a century.

Macdonald was born in Scotland; when he was a boy his family immigrated to Kingston in the Province of Upper Canada (today in eastern Ontario). As a lawyer, he was involved in several high-profile cases and quickly became prominent in Kingston, which elected him in 1844 to the legislature of the Province of Canada. By 1857, he had become premier under the colony's unstable political system. In 1864, when no party proved capable of governing for long, Macdonald agreed to a proposal from his political rival, George Brown, that the parties unite in a Great Coalition to seek federation and political reform. Macdonald was the leading figure in the subsequent discussions and conferences, which resulted in the British North America Act, 1867 and the establishment of Canada as a nation on July 1, 1867.

Macdonald was the first prime minister of the new nation, and served 19 years; only William Lyon Mackenzie King has served longer. In his first term, Macdonald established the North-West Mounted Police and expanded Canada by annexing the North-Western Territory, Rupert's Land, British Columbia, and Prince Edward Island. In 1873, he resigned from office over a scandal in which his party took bribes from businessmen seeking the contract to build the Canadian Pacific Railway. However, he was re-elected in 1878. Macdonald's greatest achievements were building and guiding a successful national government for the new Dominion, using patronage to forge a strong Conservative Party, promoting the protective tariff of the National Policy, and completing the railway. He fought to block provincial efforts to take power back from the national government in Ottawa. He approved the execution of Métis leader Louis Riel for treason in 1885; it alienated many francophones from his Conservative Party. He continued as prime minister until his death in 1891.

In the 21st century, Macdonald has come under criticism for his role in the Chinese Head Tax and federal policies towards Indigenous peoples, including his actions during the North-West Rebellion that resulted in Riel's execution, and the development of the residential school system designed to assimilate Indigenous children. Macdonald, however, remains respected for his key role in the formation of Canada. Historical rankings in surveys of experts in Canadian political history have consistently placed Macdonald as one of the highest-rated prime ministers in Canadian history.