The fictional detective in Picard’s holodeck program is Dixon Hill.
Hill is a hard-boiled private investigator created for the Star Trek: The Next Generation episode “The Big Goodbye,” which first aired in 1988. Captain Jean-Luc Picard uses the holodeck to enter Hill’s 1940s-style world, complete with a detective office, gangsters, period slang, and film-noir atmosphere. The program is designed as a historical entertainment experience rather than a real person from Federation history.
The episode deliberately draws on classic American detective fiction and cinema. Its title echoes Raymond Chandler’s The Big Sleep and The Long Goodbye, while the plot and characters include references to the 1941 film The Maltese Falcon. Hill was initially named Dixon Steele, but the name was changed because it resembled the title character of the television series Remington Steele.
Dixon Hill later returned in “Manhunt,” “Clues,” and the 1996 film Star Trek: First Contact. He is sometimes confused with famous detectives such as Sam Spade or Philip Marlowe, but those are inspirations and comparison points, not Picard’s holodeck character.