Confirmed Characters are:

Eric - The man in the "Cube." Deceased. Known to use cipher code "ConsciousHumanSouls," among others.

"Rachel" - The woman in the "Cube" calls herself this. Presumed dead. Possible identity of "The Woman/Argentina."

Charlotte - Eric's wife, also known as Lottie. Status unknown. Had a daughter with Eric. Possible identity of "The Woman/Argentina." Also goes under the alias of "Ginger"

Bill - "Rachel's" husband. Presumed dead.

Sharon - Employee and assistant at Pangent Technologies. Status unknown.

X - Employee and former assistant (now boss) of the Tumblr user and in charge of the Twitter account after The Twitter Incident. Responsible for "twitter sucks" tweet. Status unknown. Works at London office. Says "bro" and "mate" a lot. Prone to mood swings. Codename is Galahad, but is almost always called X (or redacted, or nothing). Son of Lancelot (as per Arthurian Legend).

Leslie - Employee at Pangent Technologies, assistant to X, has occasionally run the Twitter and Tumblr accounts. Status unknown. First "mentioned" in the Automatic Subtitles.

"Lancelot" - X's father, has a high security clearance. See Arthurian Legend Parallels.

Five characters seem to be mentioned by initial in the Personality Test. This was the first mention of X, but also seems to include Bill, Charlotte, Rachel, and Eric.

"Extroversion (X) is the personality trait of seeking fulfillment from sources outside the self or in community. High scorers tend to be very social while low scorers prefer to work on their projects alone."

"Conscientiousness (B) is the personality trait of being honest and hardworking. High scorers tend to follow rules and prefer clean homes. Low scorers may be messy and cheat others."

"Openness to Experience (C) is the personality trait of seeking new experience and intellectual pursuits. High scores may day dream a lot. Low scorers may be very down to earth."

"Agreeableness (R) reflects much individuals adjust their behavior to suit others. High scorers are typically polite and like people. Low scorers tend to 'tell it like it is'."     

"Neuroticism (E) is the personality trait of being emotional."