William Owen "Buckey" O'Neill (February 2, 1860 – July 1, 1898) was a sheriff, newspaper editor, miner, politician, Georgist, gambler and lawyer, mainly in Arizona.

His nickname came from his tendency to "buck the tiger" (play contrary to the odds) at faro or other card games.

On December 13, 1862, during the Battle of Fredericksburg, the senior O'Neill was wounded and served the rest of the war as a member of the Invalid Corps.

[7] During the first part of 1879, O'Neill responded to an item in the Washington Star calling for men to migrate to Arizona Territory.

On March 20, 1889, four masked men robbed the Atlantic and Pacific Railroad passenger train in Diablo Canyon.

A four-man posse, made up of O'Neill, Jim Black, Carl Holton, and Ed St. Clair, was soon formed and they took off after robbers.

There is unfounded speculation that, in 1898, William Sterin enlisted under a false name in the Rough Riders, and was killed in action on San Juan Hill.

The character of Henry Nash is incorrectly portrayed as Sterin in the TNT made-for-TV movie "Rough Riders".

The real Henry Nash was an Arizona school teacher who also served in Roosevelt's Rough Riders, and was a friend of O'Neill up until his death.

In 1894 and 1896 he ran for Delegate to the United States House of Representatives from Arizona Territory, running on the Populist Party ticket.

O'Neill led his men at the front of the line in the Battle of Las Guasimas, capturing the Spanish flank.

Theodore Roosevelt, commander of the Rough Riders, wrote about the death of O'Neill: The most serious loss that I and the regiment could have suffered befell just before we charged.

O'Neill took his cigarette out of his mouth, and blowing out a cloud of smoke laughed and said, "Sergeant, the Spanish bullet isn't made that will kill me."

As he turned on his heel a bullet struck him in the mouth and came out at the back of his head; so that even before he fell his wild and gallant soul had gone out into the darkness.

"[20] On July 3, 1907, a monument by sculptor Solon Borglum was dedicated to O'Neill and the other Rough Riders in their memory in Prescott, Arizona.

Bucky (sic) O'Neill is a main character in the TNT movie Rough Riders, portrayed by Sam Elliott.