The titular private investigator was originally portrayed by actor Tom Selleck from 1980 to 1988, and later by Jay Hernandez in a reboot developed by Peter M. Lenkov.

Often appearing in khaki pleated shorts or blue jeans, an Aloha shirt, Sperry boat shoes or white Puma Easy Rider Sneakers, ankle socks, and a battered baseball cap, Magnum was originally envisioned as a James Bond type character but, at Selleck's request,[1] was made into more of an average "everyman" with numerous character flaws.

Thomas Sullivan Magnum IV[2] is around forty years old during the original series, although a variety of birthdates are given in at least 5 episodes, ranging from August 1943 to February 1946.

While at the Naval Academy, he dated Ginger Grant who became a professional tennis player and re-entered his life in the episode "Mixed Doubles".

[5] In the episode, "From Moscow to Maui", Magnum states that he was the captain of the Annapolis football team during at least one Army–Navy game with Army scoring a touchdown early in the first quarter from a play he called.

His also develops a love-hate relationship with Jonathan Quayle Higgins III, the majordomo of the estate where Magnum was a perennial guest or "moocher".

He has free use of Masters' Ferrari 308 GTS, and he often barters with Higgins for the use of expensive cameras, the tennis courts, and other accoutrements of wealthy living.

Magnum also maintained friendships with Assistant District Attorney Carol Baldwin and Lieutenant Maggie Poole, MacReynolds' successor.

However, her death was staged presumably because General Hue had resurfaced and Michelle knew Magnum wouldn't leave Vietnam without her.

Lily Catherine appeared in five episodes of the show ("Little Girl Who", "Limbo", "Infinity and Jelly doughnuts", "Unfinished Business", and "Resolutions").

In the new series, Thomas Magnum is a decorated ex-Navy SEAL who returns home from Afghanistan, where he spent time as a prisoner of war, to become a private investigator.

[7] He gets help on cases from his two old friends, former Marines Theodore "TC" Calvin and Orville "Rick" Wright,[8] and from former MI6 agent Juliet Higgins.