A first-class citizen of Harmonia, Sinclair served in the Harmonian-Nameless War as a Harmonian soldier. He was captured by the Vague and tortured for information on the defenses of Crystal Valley. He defected to the Nameless Lands after the fall of the city and took part in the Blue Stargate Program. After a Goa'uld space station was captured by BSG-1, he was choosen to be the new commander of the renamed station of Babylon 5.