Steve Oster was a Starfleet officer in the 24th century.
In the 2370s, he was listed as a Starfleet Command officer on the dedication plaques of the Defiant-class starships. (DS9: "The Die is Cast", dedication plaque; DS9: "Valiant", dedication plaque; dedication plaque)
This character was only mentioned in writing.
He was named after production staff member Steve Oster.