Butterbur was the owner of the Inn of the Prancing Pony in Bree. He was a Man, but as Bree was inhabited by both Men and Hobbits, he had two hobbit employees: Bob, who worked in the stables, and Nob, a servant.
Butterbur appears to have had a rather bad memory, "One thing drives out another" he says. He forgot to send Gandalf's letter to Frodo, leaving Frodo uncertain as to Gandalf's fate and causing him to start his journey much later than the letter indicated. He did not remember it until Frodo and his companions arrived to stay at the inn, and even then it was long before the connection was made. He did, however, remember in time to produce Strider's credentials. In The Return of the King, Butterbur was amazed to learn that Strider, a former patron of the Prancing Pony, had become king of Gondor and Arnor.
In Peter Jackson's film The Lord of the Rings: The Fellowship of the Ring, he is played by David Weatherly, although the character is not named and most of his scenes from the book (including the reference to Gandalf's letter) are not in the film.