Markiplier

Markiplier, also known as D-9341 as his Class D code, is an adventurer, time traveler, thief, doctor, security guard, etc. He is known for getting himself into paranormal shenanigans, mainly encountering the Slender Man. He was a Class D test subject of the SCP Foundation, until gaining SCP status when he showed the powers of quick saving, reloading (essentially cheating death), and noclipping. He is also a medical doctor from Nicaragua.

Personality and attributes
Mark, at first sight, appears to be very brave (seeing as how he constantly hunts ghosts), but often runs or hides at the first sign of danger. Mark is also very mentally unstable, as he murdered a house full of his friends in Calm Time (though this may have been Darkiplier), and is extremely hostile towards Bob. He possibly has multiple personality disorder (or amnesia), as he suddenly snapped out of a fit of rage on Bob and was actually worried about him (and didn't know where he was), until he went straight back to murdering Bob as seen in the first SS2013 video. While he sometimes appreciates his fans, he sometimes insults them and is annoyed by them, as seen in A New Home.

Powers, skills, and abilities
Mark has the powers of noclipping, quicksaving, spawning objects, reloading saves, and coming back from the dead.

He is a professional doctor, trained in medical school along with Bob. He is quite intelligent, seen from his knowledge to mathematics and medical terms.

Mark is skilled in the Double Finger Defense, as seen when he deterred a monster quite easily with it.

In a fiery rage, his hair would seem to turn the color red

Asylum
For twenty years, Mark stayed at an asylum, according to Rake: Return to Asylum. It is possible that this is how he became a Class D.

Class D
During his time as a Class D, he was used to test various SCPs and he survived various containment breaches.

SCP status
Mark was given the status of being an SCP after he noclipped around a Nine Tailed Fox squad.

Tiny Box Tim
Tim is Mark's trusted companion, who always has his back.

Teddy
His childhood living toy. Mark was disturbed by him at first, but began trusting him as time went on.

Trivia

 * Although he is a Class D, he hasn't been executed for over a few years. He may have been spared due to surviving various breaches and retrieving SCPs from the site, or because of his SCP status.
 * Though, he did nuke the facility once.
 * It is unknown how he escaped from the Chaos Insurgency.
 * He seems to be used to containment breaches, and has little to no trouble with his SCP friends. He does have trouble with newly contained subjects, however.
 * He is deathly afraid of the ocean, but is often fascinated by objects and beings within.