The Honourable Sir William Mortimer Clark KC
9th Lieutenant Governor of Ontario
In office April 21, 1903 – September 21, 1908
Monarch	Edward VII
Governors General	The Earl of Minto The Earl Grey
Premier	George William Ross James Whitney
Preceded by	Sir Oliver Mowat
Succeeded by	John Morison Gibson
Personal details
Born	(1836-05-24)May 24, 1836 Aberdeen, Scotland
Died	August 10, 1915(1915-08-10) (aged 79) Prouts Neck, Maine
Nationality	Canadian
Spouse	Helen Gordon ​ (m. 1866)​
Alma mater	Marischal College University of Edinburgh
Occupation	lawyer, bank director

Sir William Mortimer Clark (also spelled Clarke), KC (May 24, 1836 – August 10, 1915) was a Canadian lawyer and politician.

Born in 1836 in Aberdeen, Scotland, Clark was educated at Marischal College and the University of Edinburgh. He came to Canada in 1859 and was called to the bar of Upper Canada in 1861.

A prominent social activist, he became a bank director and authored a number of articles on travel. In 1866, he married Helen Gordon.

Clarke was appointed the ninth Lieutenant Governor of Ontario in 1903. He supported education and hospitals during his mandate, and served until 1908. He was created a Knight Bachelor in 1907.^[1]

He died in 1915 in his summer home in Prouts Neck, Maine. His remains were brought back to Toronto, where he was interred in the Mount Pleasant Cemetery.

• Sir William Mortimer Clark archival papers held at the University of Toronto Archives and Records Management Services
• "Clark, Sir William Mortimer" . The New Student's Reference Work . 1914.