Born at Le Sueur, Minnesota on 29 June 1861, the elder son of William Worrall Mayo and Louise Abigail Wright, his wife. The younger son Charles Horace Mayo was also an Honorary FRCS. For an account of W W Mayo, their father, see the life of C H Mayo, above. William J Mayo, was educated at the Rochester High School and at Niles Academy, working in a local drug store during the vacations. When a tornado struck Rochester in 1883, W Worrall Mayo was appointed to take charge of an improvized hospital and a number of Sisters of St Francis worked with him to help the wounded. The Mother Superior proposed to build a permanent hospital in memory of the catastrophe, provided sufficient money for the purpose and nominated Mayo to take charge of it. The hospital was opened in 1889 under the name of St Mary's Hospital with thirteen patients. It was always the rule that each patient paid according to his means, that fees would not be required from charitable organizations, and that the patient's promise to pay was a sufficient guarantee. The institution quickly became known, first as the Mayo Clinic, later (1915) as the Mayo Foundation. The Mayo brothers gave $1,500,000, and on making the endowment William Mayo, speaking also for his brother, said “We never regarded the money as ours; it came from the people, and we believe it should go back to the people.” The two brothers worked throughout in the utmost harmony and to the end of their lives had a common pocket book in which each wanted the other to have the greater share. Both had the essential attribute of a true gentleman, consideration for others. At first neither brother specialized in surgery; later William was the more inclined to operate upon the abdomen, Charles upon the head and neck. Of the two “Willie” was the better administrator, “Charlie” the more original. Both were simple in their lives and actions, both were humble-minded in spite of their great success in life, and both were witty, each in his own way. During the war William, who had received a commission as a first lieutenant in the Medical Reserve Corps in 1913, was promoted major in 1917 and later colonel in the United States Army Medical Corps. During 1917-19 he was chief consultant for the Medical Service; he was appointed colonel, Medical Reserve Corps in 1920 and brigadier-general in 1921. A regent of the University of Minnesota since 1907, William Mayo was president of the Minnesota State Medical Society in 1895, president of the American Medical Association 1905-06, president of the Society of Clinical Surgery 1911-12, president of the American Surgical Association 1913-14, president of the American College of Surgeons 1917-19, and president of the Congress of American Physicians and Surgeons 1925. In 1919 he was awarded a gold medal by the National Institution of Social Sciences for his services to mankind. In 1933 he received a special award from the University of Minnesota in recognition of his distinguished services in the furtherance of scientific studies. He married Hattie M Daman of Rochester, Minnesota. She survived, him with two daughters: Mrs Waltman Walters, wife of a director of the Mayo Clinic, and Mrs Donald C Balfour, wife of the director of the Mayo Foundation. He died in his sleep at Rochester, Minnesota, on 28 July 1939, after suffering from a sub-acute perforating ulcer of the stomach, for the relief of which he had been operated upon in the previous April.