Matriarch Benezia

Matriarch Benezia is the first major boss character encountered in Mass Effect. She is a powerful Asari biotic who is the second-in-command to Saren Arterius. Like Saren, Benezia is under the "indoctrination" brainwashing effects of Sovereign. She is also the mother of Liara T'Soni, who is recruited as a squad member later in the game.

On the planet Noveria, Matriarch Benezia has managed to resurrect the Rachni, an evil race of insect creatures that went extinct long ago, by cloning them from an ancient rachni egg. The cloned Rachni Queen that they created is located in the same laboratory room where Benezia is fought. During combat, she is accompanied by Geth and Asari commandos, and used her powerful psychic abilities to form an invisible barrier around herself. After Shepard depletes the barrier by killing Benezia's henchmen, after which she is confronted directly. Here, Benezia explains how Saren has brainwashed her and briefly resists the indoctrination to give Shepard the coordinates of the Mu Relay, before becoming hostile again. Before dying, she begs Shepard to stop Saren.

Once Benezia is dead, the final matter of business is to take care of the Rachni queen. The Queen telepathically begs Shepard to spare her and promises to raise the new rachni to be peaceful, and the player gets to choose whether to let the Queen go or kill her by filling her tank with acid. It is implied that the previous rachni had actually been under the indoctrination effects of the Reapers.