Samara Morgan is loosely based on Sadako Yamamura from the original Japanese Ring series, who at her turn was inspired by the traditional onry.
Evelyn Osorio, a young woman, had a troubled pregnancy, experiencing hallucinations and visions due to her baby Samara's powers, suffering afterwards from serious postpartum depression. Evelyn tried to drown Samara when she still was a baby, but the nuns stopped her. It is revealed later that Evelyn tried to drown Samara because she told her to, supposedly because this was the only way to save Samara from the evil spirits possessing. Samara seems to have little memory of Evelyn.
Afterwards, Evelyn was taken to a mental institution and Samara was adopted by Richard and Anna Morgan.
Samara possessed the power of "projected thermography" - she can "burn" images into the mind of other living beings or on any recording media. After taking Samara home, Anna had a hard time concentrating and sleeping - her mind would be filled with gruesome images when her daughter was around. Samara's presence made the horses on the Morgan's farm go insane and die, which threw her mother into a deep depression. Samara also never slept and her adopted parents soon were terrified of her.
Anna and Samara were sent to a psychiatric hospital. Richard forced Samara to move into the farm's barn, hoping the distance between her and Anna would alleviate the visions and hallucinations. This did not work, and finally Anna Morgan attempted to kill Samara by suffocating her with a garbage bag and throwing her into a well. Anna then committed suicide by jumping off a nearby cliff. Samara was about twelve years old when this happened.
Samara lived on for seven days in the well, destroying her fingernails while trying to climb out. After she finally died, her spirit created the cursed video tape using her "projected thermography" power. Anyone watches this tape will hear their phone ring and, after answering, Samara will say "Seven days" in a ghostly voice. Exactly seven days later the viewer will suffer a terrible death unless they have made a copy of the tape.