- "Preparing this location should be no trouble at all for Marlton! Dun dun dun, engineer of destiny!"
- — Marlton
His appearance is of a stereotypical nerd in his twenties. He wears a white-collared shirt, blue jeans, glasses (which are shown to have been repaired with cloth tape in the Buried cutscene), and nice brown shoes accessorized with a pocket protector and a wrist calculator. He is covered in soot and has a few tears in his pants. He also wears a loose tie.
Marlton favors using a larger, advanced vocabulary, and thinks of himself as mentally superior to the others. He is often pedantic and smug although quite self-conscious. Marlton is very knowledgeable about weapons, often reeling off facts and critiques on the guns he acquires from the Mystery Box (though he seems to have a dislike of most of them).
Marlton suffers from claustrophobia, which is the fear of having no escape and being closed in small spaces or rooms; as well as mysophobia and germaphobia, which is the fear of contamination and germs respectively.
He has a strong emotional attachment to Misty and often compliments her. Misty has a crush on Marlton, and he reciprocates those feelings despite claiming he feels no emotion, and explains that he has a special relationship with her.
- Main article: TranZit/Quotes#Marlton Johnson
- Main article: Nuketown Zombies/Quotes#Marlton Johnson
- Main article: Die Rise/Quotes#Marlton Johnson
- Main article: Buried/Quotes#Marlton Johnson
- He is referred in game files as "
- He sometimes likes to talk about weapon backgrounds after obtaining one such as the FAL.
- He refers to the Mystery Box as the "chaos box".
- Marlton is ambidextrous.
- Marlton dislikes the Executioner, but strangely, he likes the other shotguns available.
- He is also dismissive of semi automatic and burst-firing weapons.
- Conversely, he seems to like all weapons that he identifies as of Russian origin.
- His favorite weapon is the DSR 50. This changes to the SVU-AS in Buried, although he doesn't remember exactly when.
- According to Russman, Marlton seems to have a fondness for the MTAR.
- His watch-calculator reads "190438".
- Marlton can be heard in Nuketown Zombies, by knifing the bunker in the backyard of the green house. He appears to be stuck in the shelter as he is most likely a scientist there.
- He prefers sniper rifles, as he's holding a DSR 50 in Die Rise, and an SVU AS in Buried's cutscene.
- It is revealed in Buried that he is lactose intolerant.
- Along with the Samuel J. Stulinger, Marlton can be seen as an action figure in Samantha's room during the Origins ending cutscene.