Biography: Alessa is the daughter of Dahlia Gillespie, the leader of a cult known as The Order that operates out of the fictitious titular town of Silent Hill. Alessa was born with incredible psychic powers, including spiritual intuition and premonition, leading to her being ostracized at Midwich Elementary School and branded a witch. Her only friend in childhood is Claudia Wolf, who sympathizes with her because she also comes from an abusive family background.
Dahlia becomes convinced that a certain ritual, to birth the cult's God, would likely be a success if she used her daughter as its birthmother. The technique had been performed on other girls that The Order abducted, but all previous attempts had failed. At the age of seven, Alessa is offered as a sacrifice by Dahlia to the God in the cellar of their house by immolating her body. The plan succeeds, with Alessa becoming pregnant with the deity–which remains suspended in embryotic form–but a part of the girl's soul escapes and is reborn as a baby found by Silent Hill's protagonist Harry Mason and his wife outside Silent Hill. They name the baby Cheryl.
Seventeen years after the events of the first Silent Hill game, Alessa Gillespie is reborn as Heather Mason in Silent Hill 3. Heather Mason is the main protagonist in this game.