Sir William Ernest Cain, 1st Baronet, JP (7 May 1864 – 5 May 1924) was an English brewer and philanthropist.^[1]

Cain was the son of Robert Cain, who had founded a large brewing empire, Robert Cain & Sons Ltd. He was educated at Winwick Priory.^[2] The family firm was taken over as joint managing directors by William Cain and his brother, Charles Nall-Cain, who continued to develop the business.

During the First World War, Cain donated his old home, Wilton Manor at West Kirby, to the government as a convalescent hospital for officers and paid for its conversion and equipment. He also donated money to many other war charities. For these services, he was knighted in 1917^[2] and created a baronet in the 1920 New Year Honours.^[3][4]

Cain married Florence Roberts in 1886.^[2] They had a son and a daughter. He died in 1924 at the age of 59 and was succeeded in the baronetcy by his only son, Ernest.