William Augustus Bowles (1763–1805), also known as Estajoca, was a Maryland soldier and adventurer. Seeing action as a Loyalist during the Revolutionary War, Bowles later formed an alliance with the Muscogee people and attempted to establish an independent indigenous American state with British support.

Some sources give his date of birth as 1764. Bowles was born in Frederick County, Maryland, and joined the Maryland Loyalist Battalion at the age of thirteen with the junior officer rank of Ensign, travelling with the battalion when it was ordered to form part of the garrison of Pensacola. Upon arrival, Bowles resigned his commission, and left the fortification, where he was captured by Muscogee raiders and brought back to one of their settlements.

While he was living with the Creek Tribe, a Spanish expeditionary force mustered and began to lay siege to British forts along the Gulf Coast. Bowles convinced the Creeks to support the British garrison stationed in Pensacola against the invading Spanish force, but the garrison surrendered when the powder magazine at the fortress was hit by artillery fire from a Spanish warship. The survivors of the garrison were taken as prisoners of war, but Bowles escaped into the wilderness with his Creek allies. This occurred May 9, 1781, when Bowles was either 16 or 17 years old.

After this battle, he was reinstated in the British Army and went to the Bahamas. After a few months there, the Governor of the Bahamas, Lord Dunmore, sent Bowles back among the Muscogee with a mission to establish a trading house among them. Bowles established a trading post along the Chattahoochee River. He would marry two wives, one Cherokee and the other a daughter of the Hitchiti Muscogee chieftain, William Perryman, and used this union as the basis for his claim to exert political influence among the Muscogee, later styling himself "Director General of the Muskogee Nation". Interracial marriages were common among the Seminoles and Muscogee according to historian James Leitch Wright, but historian Kevin Mulroy disagrees strongly with Wright's contention.

Pursuing his idea of an indigenous American state after the end of the Revolutionary War, he was received by King George III as "Chief of the Embassy for Creek and Cherokee Nations" and it was with British backing that he returned to Florida.

In 1795, along with the Seminoles, he formed a short-lived state in northern Florida (part of Spanish East Florida) known as the State of Muskogee, with himself as its "Director General." After designing a flag and constitution for his state, Bowles raised an army and began to carry out raids of Spanish territories in Florida. In 1800, he declared war on Spain. Bowles operated two schooners and boasted of a force of 400 frontiersmen, former slaves, and warriors.

A furious Spain offered $6,000 and 1,500 kegs of rum for his capture. When he was finally captured, he was transported to Madrid where he was unmoved by King Charles IV's attempts to make him change sides. He then escaped, commandeering a ship and returning to the Gulf of Mexico. One of the main victims of his piratical attacks was the Scottish trading firm of Panton, Leslie & Company.

In 1803, not long after having declared himself "Chief of all Indians present" at a tribal council, he was betrayed and turned over to the Spanish. William Augustus Bowles died in 1805, at Castillo Morro, in Havana, Cuba, having deliberately starved himself to death in defiance.