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Morrigan is a major companion of the protagonist in Dragon Age:Origins and a supporting character in Dragon Age: Inquisition. She's an extremally Darwinistic witch caring for nothing but her survival and gathering more magical power.
Flemeth gave her birth and raised her isolated from civilisation to be power hungry and manipulative witch.
In Dragon Age: Origins Flemeth commands her to help the Warden in saving Ferelden from the Darkspawn. She discovers her mother's grimoire and learns that she extends her life by possessing bodies of her daughters and Morrigan is next. She tries to convince the warden to kill her and steal more of her books. After the warden gathers enough of armies to fight darkspawn the final battle is close and the warden learns killing the archdemon means death of its killer. Morrigan tries to use the situation to take over the archdemon's power for herself, she was originally going to do this for her mother. If the warden is make Morrigan offers him impregnate her so her child could consume spirit of Urthemiel instead of him and spare his life. If the warden is female she tells her to convience her fellow grey warden to sleep with her. The warden can accept or refuse the offer.
In Dragon Age: Inquisition Morrigan returns as an advisor of empress Celene. If she was impregnated in the previous game she has son Kieran, who made her soft. She joins the Inquisition to help in defeating Corypheus. She informs that he seeks something in an ancient elven temple and she secretly wants to take it for herself. That's an artifact called Well of Sorrows what contains Mythal's omniscience. She can use it or the Inquisitor. Later she meets Flemeth and learns from her that she's Mythal, what makes her mother's eternal slave. She wants Kieran to be her next body and offers Morrigan her freedom for her son but she refuses realizing that would make her as abusive mother as Flemeth. After Corypheus' defeat she leaves the Inquisition and travels to unknown.