A former Marine Scout Sniper, Gibbs is portrayed as a consummate organizer, disciplined and demanding of his A-team, often standing between them and pressure from other authorities.

Gibbs' age has never been revealed, but it was shown in the episode "Heartland" that he was born in rural Stillwater, Pennsylvania. His father, Jackson Gibbs, owns a store in the same town. It has been mentioned in the episode "Frame Up" that Gibbs' father was possibly in the U.S. Army Air Force because Gibbs refers to a pin-up on his father's P-51 Mustang. He is apparently named after his father's friend, Leroy...