Sir William Mulock, lawyer, educator and Cabinet Minister, was a family friend of the Kings. Both families were Liberal and they socialized together. When Mackenzie King's father, John King, died in 1916, Mulock was a pallbearer at the funeral.
Mulock was Postmaster General from 1896 to 1905. He organized the federal Department of Labour, which was originally attached to the Post Office, and he was its first Minister. In June 1900, when Mackenzie King was travelling in Europe, Mulock sent him a telegram, inviting him to become Editor of the Labour Gazette in the newly established Department of Labour. King accepted, and always credited Mulock with bringing him into the public service. In September 1900, King was appointed Deputy Minister of Labour, under Mulock, and the two men worked closely together for several years.
In 1905, Mulock was appointed Chief Justice of the Exchequer Division of the Supreme Court of Ontario; he was Chief Justice of Ontario from 1923 to 1936. He was Vice-Chancellor of the University of Toronto (1881-1900) and Chancellor (1924-1944).
On Mulock's 100th birthday on January 19, 1944, Prime Minister Mackenzie King went to visit him in Toronto, and the press took pictures of them having breakfast together. "We toasted each other in orangeade," King wrote in his diary. "Sir William said: they will think we have been drinking whiskey." At the end of the festivities, King wrote, "I would not like to have missed this day for anything." (Diary, January 19, 1944)
Mulock died on October 1, 1944, and King was a pallbearer at his funeral.
Library and Archives Canada holds the Sir William Mulock Papers (MG27-IID11).