Annie/Dr. Gaines

Dr. Gaines is a doctor Sioux Falls hospital. He is human until a Leviathan kills him and becomes him.

Background
When he was human, he was the doctor treating Jody Mills during her stay at the hospital. Then he encounters a little girl asking if he is Dr. Sexy. She soon grabs his arm and kill him. The Leviathan, who was the little girl, transforms into Dr. Gaines.