An now, an Ohio woman believes her daughter was also influenced by the character.
Her mother says her writings and drawings have always been dark, referencing demons, being insane, falling into darkness.
Never did the 13-year-old's mother imagine her daughter would want to become one of the characters he frequently referenced.
"I came home from work one night and she was in the kitchen waiting for me and she was wearing a mask -- a white mask," she said.
The daughter had a knife and began attacking her mother in the kitchen.
Now, after hearing about the Wisconsin 12-year-olds accused of stabbing their friend 19 times because they wanted to please Slenderman.
This mom thinks the fictional horror character also had an influence on her daughter.
The daughter's writings have referenced Slenderman and also referenced killing.
This was a wakeup call for this mom, and she thinks it should be a wakeup call for all parents.
"We have to police what they do and what they read," she said.
The daughter is in a juvenile center. Officials believe the Slenderman character was invented in a contest, and that his legend grew among paranormal fans.