Steve Oster was a member of Starfleet in the 24th century.
In 2370, Oster was listed as a Starfleet Command official on the dedication plaque of the starship USS Defiant. (DS9: "The Die is Cast")
In 2375, Oster was listed under the same category on the dedication plaque of the USS Sao Paulo. (DS9: "The Dogs of War")