William Hamilton Merritt III (June 8, 1855 in St. Catharines, Ontario – October 26, 1918) was a Canadian soldier, author, and mining engineer. His grandfather, William Hamilton Merritt, was a politician in Ontario. Confusingly, his father and cousin also shared his name; even though he is now known as William Hamilton Merritt III, during his life, he did not refer to himself as the third.