Evelyn was the mother of Samara Morgan, and for a majority of her life a patient in a mental institution. She is mentioned and shown in The Ring 2 which explains it all: she came to a catholic hospital pregnant with Samara, claiming that the father was a demon from the sea. One night, she attempted to drown Samara, but the nuns took the baby away from her arms. She is believed to be insane because she claims her child is not human at all and is fully evil. She was locked away in a mental institution and died before she could see the day Samara comes at rest.
The Ring TwoEdit
Many years later, when Rachel was on Samara's trail in order to rescue her son, she visits Evelyn in a mental hospital, where she found the way to end Samara's curse. Whatever happened to Evelyn after that is unknown. In the past, she was a frail and plain girl at the age of 19 wearing a silky white dress and barefoot. Her hair was long and unkempt. In the later years, she is a witch-like elderly patient living in a unkempt room with papers thrown about, especially around her desk.
She also claims that her attempt of drowning her daughter was instructed. Evelyn says that her daughter told her to drown her, also claiming that she listened. Evelyn advises Rachel that she must listen in order to save her son. Yet along with that said "You let the demon get in." In the beginning of the visit, Rachel is able to hear the melody Evelyn in portraying. She confirms that she is familiar with it and the man beside her says "They all do." Possibly meaning that the people who have watched the tape are able to hear this melody in their dreams and such, or that there are other people who have come to see Evelyn over the subject.
Evelyn later died from an unknown cause. Her ghost began to haunt a nearby church. More about her backstory was revealed in Rings. Evelyn wasn't raped by a sea demon who fathered Samara, but a priest named Burke at the church. Burke kept Evelyn locked away beneath a bell tower until she was found and taken to the hospital where she gave birth to Samara. Burke was eventually killed by Samara. It is implied that the trauma of her pregnancy is what caused Evelyn to think her child was possessed by a sea entity. How Samara obtained her powers is still unknown.