Short answers, pulled from the story.
Orestes was a Roman general and politician of Pannonian ancestry who rose from serving as a secretary in Attila the Hun's court to becoming the dominant power in the Western Roman Empire. He elevated his own son Romulus to the throne in 475, making the boy the last recognized Western Roman emperor. Orestes was captured and beheaded on the 28th of August 476.
Orestes served as a notarius, or secretary, in Attila's administration from at least 449, becoming one of Attila's most trusted lieutenants. In 449, Attila sent him twice to Constantinople alongside an ambassador named Eslas to conduct diplomatic negotiations with the Eastern Roman court.
In 475, Emperor Julius Nepos appointed Orestes to the dual offices of magister militum and patricius. By the 28th of August 475, Orestes marched on Ravenna at the head of the foederati levies, and Nepos fled to Dalmatia without offering military resistance.
Romulus Augustulus was the son of Orestes and the last recognized emperor of the Western Roman Empire, elevated to the throne in 475. He was called Augustulus, meaning 'little Augustus,' because he was still a child at the time of his accession.
Orestes was killed following a rebellion by Odoacer, a Germanic commander whose troops demanded land grants in Italy as compensation for their military service. Orestes, as the real power behind the western throne, refused to authorize those grants, triggering the revolt that ended his life.
Andrew Pleavin played Orestes in the 2001 television miniseries Attila, which depicted his service to the Hunnic king. Iain Glen later portrayed him in the 2007 film The Last Legion, though the filmmakers acknowledged that film departs significantly from the historical record.