Matriarch Benezia is not only an adversarial character for Commander Shepard, but the mother of one of Shepard's party members, Liara T'Soni. In the Asari culture, some women, when they get toward the end of the long life, become Matriarchs. These Asari are influential leaders and teachers, who become mentors to younger Asari. As Asari can live up to one thousand year lives, the Matriarchs can be very influential to their followers. Benezia was one Matriarch with a devoted following who saw the problem of humanities sudden and powerful arrival into Citadel space as an event that required her influence and teachings so that humanities integration could be peaceful and beneficial to all the citadel races. She allied herself and followers with Saren, understanding him to be both influential in the counsel but antagonistic to humans in general. If she could guide his beliefs so that he put his considerable power and resources to the purpose of helping to incorporate humanity into the Citadel worlds, she would have accomplished a considerable feat for the betterment of the Citadel worlds.
Unfortunately for her, Benezia does not know until it is too late that Saren is being more and more controlled and manipulated by Sovereign, the arrogant and sinisterly plotting member of the Reapers. Sovereign, a vanguard Reaper left behind of unknown origin but of technical ability far beyond current science, is an artificial intelligence acting as Saren's own ship and using technology to control Saren and all on the ship. In her effort to influence Sovereign, Benezia and her followers also fall under Sovereign's campaign of mind control and get turned toward Sovereign's goal of bringing back the Reapers.
However, Benezia is an Asari Matriarch and possesses an unequalled mind. On some level, she realizes things are going wrong and in some part of her subconscious, carves out a space for her true, uncontrolled character to remain intact when she needs to communicate the truth one last time. She accesses that part of her before her death at the hands of Shepard on Noveria and gives him important information before losing control of herself and again attacking Shepard.
Her relationship with her daughter, Liara T'Soni is strained, and Liara, when she learns of her mother's alliance with Saren, is determined to stop her. Liara seems to have felt Benezia to be a distant mother and the two were never close. Liara also does not know who Benezia mated with so the identity of Liara's other parent, Benezia's partner at least for the conception of her daughter, is not known.
Benezia is a tragic character in that her intent was to influence Saren to be more constructive in his approach to humanity and the future of Citadel space. She brought her followers to him in the hope of creating a group of influential leaders to help the Citadel's future, but instead created a highly intelligent army of powerful Asari with access to cutting edge technology that could help bring about the apocalypse of Reaper return.
Matriarch Benezia is voiced by former Star Trek: The Next Generation star Marina Sirtis.