What was the Spanish representative in Washington that helped construct the Adams-Onis Treaty?

The Spanish representative in Washington who played a key role in constructing the Adams-Onís Treaty was Luis de Onís. As Spain's minister to the United States, he negotiated with U.S. Secretary of State John Quincy Adams, ultimately leading to the treaty in 1819. This agreement settled border disputes between the U.S. and Spain and resulted in Spain ceding Florida to the United States.