Ford Prefect was the product manager for the artificial intelligence division of the Sirius Cybernetics Corporation.

Prefect's signature was on a certificate naming Ira Graves as "humanoid of the year" in gratitude for his contributions to the Proxima Centauri Interplanetary Bowling League (and also their marching band). (TNG: "The Schizoid Man")

This character was only mentioned in writing.
Prefect's name was only visible on a piece of background artwork decorating the set of Graves's office. The certificate, as it appeared on-screen, is printed in The Continuing Mission, a reference work
Both Ford Prefect and the Sirius Cybernetics Corporation are references to The Hitchhiker's Guide to the Galaxy, though the original Ford Prefect was not associated with the Corporation. The original Prefect, (while Human-looking), was said to be a Betelgeusian.