William Cooper was an Aboriginal activist and spokesman for the Yorta-Yorta people. He spent his early life working in the pastoral industry as a shearer and a handyman. At one point he was sent to Melbourne to work as a coachman for the politician, Sir John O'Shanassy, before returning to various pastoral jobs. He was married three times during his life and had several children. One daughter was the matron of the first Aboriginal Hostel in Melbourne, one son fought and died in World War I, another son was a gifted sprinter.

While Cooper was a member of the Australian Workers union during the droughts of the 1920s and the Depression of the 1930s, he became a spokesperson for the Indigenous people in central Victoria and western New South Wales, advocating aid for his people, but none was ever received.

In 1933, he moved to Melbourne where he became involved in the Australian Aborigines League. While there he wrote a petition to King George VI in 1937, asking for improved conditions for Indigenous Australians, the vote for Aboriginal people and Aboriginal electorates in federal parliament. He managed to get 1,814 signatures from Indigenous Australians across Australia and led a delegation to the Prime Minister, but the Australian Government refused to send the petition to the King. It was Cooper who proposed holding a day of Aboriginal Mourning on Australia day, and it was done to co-incide with the 150th aniversary of Australia Day.

William Cooper spent his remaining years protesting the State government's treatment of the Indigenous Australians still living at Coranderrk, Cumeroogunga and similar places, comparing them to the higher standards of living and the rights Maoris and Canadian Indians received in their own countries. In 1940, Cooper retired to Barmah, Victoria.

Source: Australian Dictionary of Biography: Online Edition