Mother: Patricia "Trish" Rabb(later married again and changed last name to Burnett)
Father: Lieutenant Harmon Rabb, Sr.(deceased)
Stepfather: Frank Brunett
Half-brother: Sergei
Grandmother: Sarah Rabb
Date of Birth: October 25, 1963
Place of Birth: La Jolla, California
Height: 6 feet, 4 inches
Weight: Approximately 180 pounds
Hair color: Officially black, but appears more brown
Eye Color: Blue
Current Location: Washington, D.C.
Current Occupation: Navy JAG Lawyer/Navy Aviator
Currently Stationed: JAG Headquarters, Falls Church, Virginia
Current Rank: Commander
Social Security Number: 989 54 8301
Educated: Annapolis Naval Academy
Interests: Playing his guitar and singing, building cars occasionally, flying his plane, "Sarah", which is named after his grandmother
Extraordinary skills: Flying nearly any aircraft, picking locks, expert marksman, expert in maritime law.
Biography (Mostly spoiler-free):

Harmon Rabb, Jr., usually called "Harm" or "Rabb" by his acquantinces, was raised to be an aviator in the Navy. His father, Harmon Rabb, Sr., was one of the best pilots in Vietnam. Rabb, Sr.'s call sign, Hammer, was one of the most respected call signs in the entire war. Unfortunately, Rabb, Sr.'s plane was shot down and Rabb, Sr. was declared MIA. Harm received word of this on Christmas, 1969. However, he didn't give up his desire to become a naval aviator. If anything, it made him more determined.

Harm made it to the academy around 1981. His best friends at the academy were his roommate, Keeter(see Smoked and Black Jet), a classmate, Diane Schnoke(see Death Watch), and another classmate, Sturgis Turner(see his biography). After graduation, Harm continued his dream of becoming an aviator by entering the Naval Flight School. His roommate there, Lucas Pendry(see Pilot Error), grew very close to Harm and they became best friends.

Harm became an aviator and started flying missions until, during a night trap, he crashed and his RIO was killed. His wings were removed and he joined JAG after studying law. But, during one of his cases, he was diagnosed with night blindness, which showed that the crash wasn't the fault of his flying skills. He was given back his wings, but he stayed with JAG, mostly because he couldn't fly the mandatory night missions required of an aviator.

Paired with a Naval Lieutenant(J.G.), Meg Austin, for one year, Harm went on a variety of exciting missions around the world in addition to his regualar duties. His commanding officer, Commander Lindsey, was rather inept and transferred out of JAG Headquarters after a year.

Harm, after losing both Meg and Lindsey, became one of the senior lawyers at JAG Headquarters and was paired with a Marine Major, Sarah "Mac" Mackenzie. Over the next several years, they have done everything from spying, to resigning their commissions, to becoming the temporary Judge Advocate General, and much, much more, as well as their usual duties prosecuting and defending huge amounts of crucial and exciting cases.

In order to not give away too many spoilers, I have not included much information from the time during the episodes.