Marilyn Monroe was a famous actress and sex symbol in the middle of the 20th century, and an icon of glamour and beauty for centuries after.
Appearances in Red Dwarf
Posters of Monroe adorned the lockers of Lister and Rimmer's original sleeping quarters in the first two series. The Cat would sometimes read magazines featuring her.
In the "Better Then Life" Total Immersion Video Game, The Cat fantasized her as one of his many girlfriends. (RD: Better Than Life)
Kryten's present...
Olaf Petersen was apparently also a fan, as he purchased a build-it-yourself kit droid in her likeness while on planet leave on Callisto. Lister would later put the robot together as a present for Kryten's last night, since he would be soon replaced by Hudzen-10. Though the Monroe droid looked nothing like Marilyn, Kryten believed it to be a dead ringer for the real thing. It was defective, smashing through the wall and going walk-about. (RD: The Last Day)
A Waxdroid version of Monroe was a member of Rimmer's fighting force on Waxworld. She was killed during the assault on Villainworld headquarters. (RD: Meltdown)
In Infinity Welcomes Careful Drivers, Albert Einstein had an affair with Marilyn Monroe while he was developing his theory on stasis booths. He abandoned the theory because he spent the rest of his life taking frequent cold showers.
Notes
Debbie Ash, the actress who played Marilyn in the episode "Better Than Life", caused numerous smeg-ups as she couldn't do the "boop-boop-be-doop."
The robotic version was played by Julie Higginson.
The Waxdroid version was played by Pauline Bailey.