Dorothy Duncan was an Arkham Asylum inmate posing as a member of the staff. She was later trampled to death during the prison riot.
Posing as Arkham staff
After the institution closed, Duncan resided in the basement, and later pretended to be staff when it was re-opened. She subsequently freed all the inmates, and it was discovered that she was a victim of Jack Gruber, who performed Electroshock therapy on her with two metal pins. She died after being trampled by the freed inmates.