If an answer from the 1700s would help, there's the story of William Augustus Bowles, also (not entirely correctly) known as Billy Bowlegs. He was a former loyalist from Maryland who fought in the Revolutionary War, then served the Royal Navy (on and off) as a privateer in Florida and the Caribbean. He harassed Spanish ships and helped defend the British garrison in Pensacola.
He married two women, one from the Creek Confederacy, one from the Cherokee, and (after a brief career as a comedian and merchant in the Bahamas) attempted to establish a pan-Native American state in what's now the Florida Panhandle, called Muscoge or Muskogee.
He did visit King George as the "Chief Ambassador for Creek and Cherokee Nations," won a promise of military aid against America, then returned to Florida, declared war on Spain... and was promptly captured by the Spanish. He died holding a hunger strike in a Havana prison in 1805.
His state had attracted citizens from the Creek, Cherokee, and Seminole, as well as runaway slaves and "disaffected whites," and could possibly have been quite influential, although Bowles' capture came in part thanks to Col. Alexander McGillivray, a rival leader of the Upper Creek who had cut some deals with the Spanish and the Americans, and in part because Bowles kept overstating his influence, including calling himself "chief of all Indians present" at a big meeting.
Levi General was the spokesperson of the Iroquois Confederation at the League fo Nation. He even travelled with an Iroquois passport.