Aerie

Aerie is a Lawful Good Cleric/Mage (technically an illegal class combination for an Elf) who can be recruited in BG2. With the ability to cast the majority of spells available within the game, she makes a good addition to a party which would otherwise be low on healing and offensive magic.

Baldur's Gate 1

Aerie does not appear in BG1.

Siege of Dragonspear

Aerie does not appear in SoD.

Baldur's Gate 2

Aerie can be found in the circus at the beginning of chapter 2. She will offer to join your party and has no side quests of her own, though recruiting her will potentially lead to a quest from another NPC. She gets on with most good and neutral companions, although sometimes they may tire a little of her complaints (especially Jaheira). Do not keep her in a party with evil companions, as they are likely to say something which upsets her and then you will have to choose between them.

Romance

If your character is male and elven, half-elven, human or gnome, he can enter into a romance with Aerie. The romance dialogues start soon after you recruit her, and move on quite quickly (unlike Jaheira's romance, which is slow and drawn out).

The key to romancing Aerie is to listen carefully to what she says, and sympathise over the loss of her wings. Do not push things too quickly or flirt as she wants to take things at an almost glacial pace, particularly in comparison with other companions. Basically you have to act as her protector more than her lover until quite late on in the game.