Crewman third class Foster was an operations division United Earth Starfleet officer who served on board Enterprise NX-01 during the 2150s, under Captain Jonathan Archer.
In 2153, Foster served as a security guard for the two assimilated Tarkaleans in sickbay which were transported from their freighter. When the Tarkalean male woke up and Doctor Phlox was up to inject him a sedative, Foster tried to help Phlox but was hit and then thrown through the room against a rack by the Tarkalean female.
When Foster woke up, Phlox had been infected with nanoprobes. Foster himself was not infected as Phlox told him after a scan.
Foster later assisted Phlox by pushing the activation button of the imaging chamber so Phlox could be treated with omicron particles. (ENT: "Regeneration")
Foster was played by stunt actor Paul Scott. He was not identified in dialogue but is listed as "Foster" in the end credits of the episode.