- "You know... Clarence... that's not a bad handle - I am something of a guardian angel."
Clarence named himself while going through the "space" in Philip's mind when he came about a section devoted to film titles. He states that Philip has not only seen 3,103 and 1/2 movies, but also that Philip only watched the first half of "It's a Wonderful Life" and states that he now will never know how the movie ends. This is where he gets the name Clarence from as he states he is somewhat of a guardian angel.
He is first heard in the sewers, where he transports Philip to a dreamworld where he must solve some puzzles. After that, he constantly taunts Philip throughout the game, calling him a "monkey" and insulting the human race, hinting that the Tuurngait's "hive mind" intellect is superior to mental individualism. Twice he calls enemies to attack Philip, once with Dr. Eminess in the computer room, and once with an infected that bursts through a door in one of the hallways. Residing in Philip's mind, Clarence apparently has the power to manipulate or even block out vision, which he uses to trick or frighten Philip with imaginary enemies. Though originally he seems to be solely dedicated to 'freeing' himself by getting Philip killed, he eventually switches gears and decides to try to convince Philip to at least share control of his body with him.
Clarence is forced out of Philip's mind when the cure is injected, but the machine transfers Clarence into a nearby infected corpse. He revives the body and tries to get revenge on Philip for attempting to kill him, but is killed by the Tuurngait (as his self-consciousness was destroyed upon being reintegrated with the Tuurngait, the only way it can be referred to is as a killing). Immediately following this, they stop attacking Philip. Philip notes in his final message that he has more in common with Clarence than the Tuurngait.
Clarence has been theorized to have existed in Red's body as well, though it is extremely unlikely. Most bacteria and viri are destroyed by extreme heat, and even if they weren't, it begs asking how the virus could have possibly passed from Red to Philip. There is also the fact that in Philip's first contact with Clarence, he is non-sapient; only the voice of a much larger organism. It is more likely that Philip was infected elsewhere, either through the air (the Tuurngait is speculated to be an airborne virus due to the way many personnel contracted it without any prior contact with infected individuals), or through contact with the Tuurngait Infected who knocked him unconscious at the conclusion of the first game.
Also, Clarence said (in Penumbra: Black Plague) that we, meaning the Tuurngait as a whole, would not let Red die. This suggests that the Tuurngait were in contact with the splinter of itself within Red, which, in turn, suggests that Red was infected in a completely different way.
- See: Quotes