Alianna was a priestess of Bhaal, the protagonist's mother and allegedly Gorion's friend and 'occasional lover'. Her race changes depending on which race the protagonist has.
Baldur's Gate: Siege of Dragonspear[]
In the Ruined Temple of Bhaal, now dedicated to Cyric, Madele confirms that Gorion and Alianna were lovers. Gorion attempted to reform Alianna, believing his love could change her. Madele says that "passion led him to careless speech, and she brought his words back to the temple," implying that Alianna may have seduced him to gather information on the Harpers. Gorion begged Alianna not to sacrifice her own child to Bhaal before one of Gorion's allies shot her in the throat with an arrow.
Baldur's Gate II: Throne of Bhaal[]
Alianna appears as a ghost in the Pocket Plane, alongside the ghost of Gorion, after the player kills Yaga-Shura. She reveals her true identity as a priestess of Bhaal, how she came to be the mother of a Bhaalspawn and how Gorion killed her.
This means that Gorion lied in the letter the player finds in the first game, where he stated that she died in childbirth.
Possible Plot-Hole[]
Either the information given is a lie or it creates a plot-hole. Her statement implies that she was still alive during the Time of Troubles and that she gave birth and died around the same time. That would mean the protagonist is just about ten years old during the time the games take place, which they are clearly not.