William Lyon Mackenzie
William Lyon Mackenzie (March 12, 1795–August 28, 1861) was a Canadian journalist and rebel.

In 1834 he became the first mayor of Toronto, and in 1836 he founded the newspaper, The Constitution, to promote the policies of his Reform Party. In 1837 he led the Upper Canada Rebellion against Sir Francis Bond Head and the Family Compact, which was quickly put down. Mackenzie escaped to the United States, and set up a provisional government on Navy Island in the Niagara River. He was later imprisoned in the U.S. for his involvement in the Caroline Affair. An amnesty allowed his return to Canada in 1849, and he was a member of the Legislative Assembly of the Province of Canada from 1851 to 1858.
William Lyon Mackenzie was the grandfather of William Lyon Mackenzie King.