Magnum, Everyman

from Wiki as I prep a Halloween costume.

In real life more going for Robin Masters, “the celebrated-but-never-seen author of several dozen lurid novels.”

A recurrent theme throughout the last two seasons, starting in the episode “Paper War”, involves Magnum’s sneaking suspicion that Higgins is actually Robin Masters since he opens Robin’s mail, calls Robin’s Ferrari “his car”, etc. This suspicion is never proved or disproved, although in at least one episode – “Déjà-Vu” S06E02 – Higgins is shown alone in a room, picking up the ringing phone and talking to Robin Masters, indicating they are two different persons.