Thomas Sullivan Magnum IV was born 1944. Both his father and grandfather were naval officers.
He was born in Detroit, but raised in the region of Tidewater, Virginia. In high school, his football team won a Virginia State football championship. Some members of his family, including his mother and her second husband, still reside there.
Magnum attended the United States Naval Academy then served ten or more years as an officer in the United States Navy, rising to the rank of Lieutenant before resigning from the service in disillusionment in 1979.
Magnum was a Vietnam War veteran and a former POW who believed his wife Michelle died in bombing during the final pull-out from Saigon. He served in both the SEALs and Naval Intelligence during his Navy years, and as such maintained many contacts in both communities.
After he retired he moved to Hawaii where he became a Private Investigator. He ended up working for Robin Nest as security personnel, in exchange of room and board, and use of his Ferrari. His boss was Higgins, who he suspected of being Nest, but could never prove it.
When he was shot defending Higgins, he found out at least some of Higgins’ secrets and accepted being Turned.