Liara T'Soni

"By the goddess"

- Liara

Background
Liara is a Prothean scientist from Mass Effect. After saving her she joined Shepard's team, and then became an ally to help fight Saren. She's a pureblooded Asari, meaning both of her parents were Asari, which is usually looked at negativly because they aren't getting the best of both races. She is the daughter of both Matriarch Aethyta and Matriarch Benezia. She only 106, hardly a child by Asari standards. She has a strong power of biotics, and a great knowledge of the Protheans by studying them over the years.She is a potential romance for both Male and Female Shepard.

Mass Effect
Knowing that Matriarch Benezia had a daughter, Commander Shepard  was suppose to find Liara T'Soni to see what she knew about her mother. So he/she went into the Artemis Tau cluster, then eventually found she was at a Prothean dig site on Therum. The geth were following Liara in an attempt to either kill her or join Saren. They chased her to a barrier curtain where you first meet her. After getting behind the curtain, Shepard saves Liara, but then they meet more of Saren's men on their way out of the ruins. Shepard and the others including Liara escape the dig site as it collapses on itself. Liara joines the Normandy, becoming apart of the crew, and a squadmate. She is able to intercept Shepard's visions from the beacon and help make sense of them before Saren gets the conduit. She believed the Protheans weren't the only race to have lived before the galaxy came together, and when Shepard told her about the Reapers, she realized it was the truth.

Mass Effect: Paragon Lost
In Mass Effect Paragon Lost Treeya Nuwani asked Liara T'Soni for knowledge on a strange artifact found on Fehl Prime. Liara after analzying the artifact tells Treeya it is Reaper technology, and then tells Treeya all about the Reapers, explaining they killed the Protheans.She also says that Soverign was in fact a Reaper. Although the others have their doubts, they have enough respect to Liara to take the Reapers seriously enough.

Mass Effect 2
Liara isn't a main squadmate on Mass Effect 2, although incounterable. She in the DLC Lair of the Shadow Broker has a much larger role.

Mass Effect 3
Liara comes back full time as a squad mate in Mass Effect 3. She plays a big part in the Crucible and documenting it in case the Reapers win. You can continue your romance with her, have her on your squad, and if she lives she continues her work as a Shadow Broker in the resolution.