Foster was a 22nd century Human, an Earth Starfleet officer assigned to the starship Enterprise as a security guard. In 2153 he was posted to sickbay by Lieutenant Reed to guard the two assimilated Tarkaleans. However he and Dr. Phlox were over-powered, and Phlox got infected with nanoprobes. Later he guarded Phlox and assisted him with his treatment. (ENT episode: "Regeneration")