Stein was a Starfleet officer in the 24th century.

As of 2375, Stein held the rank of Commander, and was assigned to Starbase 19. Stein presumably was killed when the starbase was attacked by Dominion forces early in that year. (TNG novel: The Battle of Betazed)

Stein was likely the executive officer of starbase commander Admiral Georgianos, though this is never explicitly stated.
Starbase 19 personnel
UFP seal GeorgianosArlen GloverHiram KawakamiSteinth'Vraas Starfleet Command logo