Lieutenant junior grade Foster was a Starfleet Academy cadet who was on a training mission aboard the USS Enterprise in 2285.
While the Enterprise was returning to Earth following a confrontation with Khan Noonien Singh, Foster asked Admiral James T. Kirk if there would be a ceremony or reception celebrating Enterprise's return – "a hero's welcome", as Kirk put it. The admiral, still reeling from the recent death of Spock, said in reply to Foster, "God knows there should be. This time we paid for the party with our dearest blood." (Star Trek III: The Search for Spock)
Foster was played by veteran Star Trek actor Phil Morris.
In the first draft script of Star Trek III, Foster was given the rank of midshipman, rather than cadet.
According to the novelization, Foster was an electronics specialist and had maintained the navigational computer during the battle against Khan.