William Henry "Bully" Hayes (1827 or 1829 – 31 March 1877) was a notorious American ship's captain who engaged in blackbirding in the 1860s and 1870s.

Hayes operated across the breadth of the Pacific Ocean from the 1850s until his murder on 31 March 1877. He has been described as a South Sea pirate and "the last of the buccaneers". However, in their account of his life, James A. Michener and A. Grove Day warn that it is almost impossible to separate fact from legend regarding Hayes; they described him as "a cheap swindler, a bully, a minor confidence man, a thief, a ready bigamist", and commented that there is no evidence that he ever took a ship by force in the tradition of a pirate or privateer. Hayes was a large man who used intimidation against his crew, although he could reportedly be very charming if he chose to be.

He was born in Cleveland, Ohio, one of three sons of Henry Hayes, a grog-shanty keeper. Hayes became a sailor on the Great Lakes after running away from home. He is believed to have left New York as a passenger of the Canton on 4 March 1853, although when the ship reached Singapore on 11 July 1853 it was captained by Hayes, and sold by him there shortly after arrival. Hayes operated in East Asia, carrying out various frauds on ship's chandlers over mortgaging ships, providing forged papers in payment for cargo, and selling cargo for his own account rather than for the account of the owners of the cargo.

Hayes arrived in Fremantle, Western Australia in January 1857 as captain of the C. W. Bradley, Jr. (which was the Canton, repurchased and renamed). The Bradley had excellent cabin accommodation, and made two trips to Adelaide in March and June 1857 with passengers. The South Australian authorities were not pleased as many of these migrants were convicts with conditional pardons. The Singapore ships chandlers caught up with Hayes in Perth, Australia and forced the sale of his ship, bankrupting him. The Bradley was sold in Adelaide on 22 July and was later renamed Federation.

Hayes married the widow Amelia Littleton in the Clare Valley town of Penwortham on 20 August 1857, bigamously if, as is believed, Hayes had earlier married in the United States.

Hayes had built up debts in Adelaide, but by a ruse escaped his creditors and in Melbourne, Australia he gained the command of the Orestes sailing to Vancouver, Canada. Hayes was thrown off the ship in Honolulu by the supercargo for swindling passengers. He proceeded to gain command of a new ship, the 318-ton brig Ellenita with a cargo obtained by fraud. Hayes sailed back across the Pacific, abandoning Amelia in San Francisco. Another version has her falling from the Orestes in 1858 and drowning. On the return trip to Sydney, Hayes lost the Ellenita off Navigator Islands on 16 October 1859 and with the women and children and a skeleton crew reached Savaiʻi to raise the alarm. After considerable difficulties, the remaining passengers and crew were returned to Sydney by H.M. brig Elk. There Hayes evaded a charge of having indecently assaulted one of the passengers, Miss Cornelia Murray, aged 15.

Although Hayes lost the Ellenita in a storm and others to creditors, he always found new ships to command and new cargoes to fraudulently acquire and sell. Between maritime adventures Hayes became a member of a blackface minstrel troupe in New South Wales, Australia.

Hayes was a notable early figure in the history of the Otago region of New Zealand. After facing bankruptcy in Australia in the late 1850s, he sailed to Otago in 1862 (at the time the region was the centre of a gold rush). He toured the region with a travelling company of vaudeville artists on a tour of New Zealand. In January 1863 they arrived at Arrowtown. Hayes married a widow Mrs Roma 'Rosie' Buckingham, whose four sons were vaudeville artists, performing as The Masters Buckingham. Hayes and Roma settled in Arrowtown where he opened a hotel, the "United States", later called "The Prince of Wales". The nearby Lake Hayes is indirectly named for him; originally called Hay's Lake after an early settler, the spelling changed over the years as locals came to associate the name with that of Bully Hayes.^{[citation needed]}