Dr. Phil

Dr. Phil is a strange, demon-like entity who physically manifested in a sewer sometime in the 60's or 50's. He is a single cell organism, and his only cell is a red blood cell. The physical form you know him for having is not actually his true form; nobody knows what his true form is, but it is possible he has many. He is worshiped by many Satanists out there, as he is a sewer clown, a type of demonic entity. 
His hobbies include murdering spoiled little shits, vandalism, pretending to be a doctor because he got a PhD in savagery. He has committed theft multiple times as well, but he is in denial of it. 
Presumably, he cannot be killed, as he has had many experiences where he should have died, but, alas, he is still alive and well. When he gets too close to perishing all the hairs on his body dissipate, causing his mouth to disappear as well, becoming Dr. Bald. Dr. Bald is an even more powerful entity. Nobody knows his true power level, but it is known he is more powerful than Sans Undertale, so he must be godlike. He was even able to kill Colonel Sanders, so you know he's fucking scary. Dr. Bald, however, is able to be killed, as long as you read him bad Mpreg fanfiction off of Archive of Our Own. He disintegrates upon hearing anyone but himself read it aloud.