Chief Homer J. Chief commands T.H.U.M.B. (Tiny Human Underground Military Bureau), an intelligence agency established after agents Tom and Swinging Jack were shrunk to three inches by a laser accident. His title "Chief" coincides with his surname, creating the redundant name Chief Homer J. Chief. He maintains a perpetually grumpy and irritable disposition, frequently displaying frustration toward subordinates—especially during Tom and Jack’s mission briefings.

Physically, he is a heavyset man with a thick mustache. As a U.S. Intelligence superior, he deploys the shrunken agents against M.A.D. (Maladjusted, Anti-social, and Darn mean), assigning operations that employ miniature vehicles and scaled equipment. He directs Tom and Jack from standard-sized environments while they navigate reduced-scale settings. His role, background, and temperament remain consistent throughout the series, with no documented evolution. The phrase "For the last time, Feller..." appears in an episode title but is not confirmed as his dialogue.

T.H.U.M.B. originated directly from Tom and Jack’s shrinking incident, formalizing as the agency’s name. Chief Homer J. Chief has overseen the bureau since its inception, focusing operations solely on thwarting M.A.D. His leadership persists unchanged across the series.