Liara T'Soni

Dr. Liara T'Soni is an asari researcher who has spent her life of roughly a century (about 1/10th the typical asari lifetime) studying Prothean technology and culture. She is a highly trained user of biotics and bears the unique asari scientist class, which is similar to adept but with less direct combat ability.

Storyline Details
Shepard is given a mission to find Liara upon becoming a Spectre, and eventually finds her suspended in a field of energy at the dig site on Therum in the Knossos system of the Artemis Tau cluster. She joins Shepard after being rescued and is then available as a squad member. Her primary role is to help with vision interpretation in order to stop Saren in time. She is also a potential romance interest for characters of either gender. It should be noted that you can recruit her long after the Citadel, making it easy to ignore her romance and character in general. It is even easier to miss her companion achievement; you must do little more than the required Citadel quests before doing her mission and making her a permanent companion.

Family Relations
It is revealed that Liara is Matriarch Benezia's daughter, though she has shied away from her mother's life as an important figure in galactic affairs. Liara prefers to keep to herself, and is in fact a bit awkward around people. However, she knows her mother well enough to be astonished to discover she is working with Saren, and does not believe she could be truly aiding him of her own free will. It is also revealed through conversation with Liara that she does not know who her "father" is, but only that she was also an asari, which is apparently frowned upon and might contribute to Liara's behaving like an outcast from society. Whomever it was, she does not wish to be identified -- whether this is important and will be revealed in future installments is unclear.

Noveria
Soon after landing on Noveria it becomes apparent that the Matriarch is "visiting" a research complex near Port Hanshan. If Liara has been recruited but is not present, a squad member will suggest that Shepard bring her to confront her mother. Be advised that doing so could easily jeopardize any companion/ally achievements you are attempting. If you do bring her along you are rewarded with extra dialogue, and upon regaining her true self the Matriarch confides that she has always been very proud of Liara, calling her "Little Wing" before expiring.