Tiax

Tiax is a gnome found near the Flaming Fist headquarters in Baldur's Gate at 1440, 1610. He does not have a quest which needs to be completed if you want him to stay in your party for a long time. His starting equipment is a mace, leather armor, a sling and 15 bullets. He has delusions of grandeur, believing he is chosen by Cyric to achieve world domination.

Tiax's special ability is Summon Ghast, which is very useful against Basilisks and Sirines because they are immune to petrification and charm due to beign undead. Despite his slow movement, the Ghast is also one of the best offensive summons because it has 3 attacks per round that can paralyze opponents with successful hits unless target saves vs death and cause disease unless target saves vs breath.

Baldur's Gate II
In Shadows of Amn, Tiax is in a cell in the Asylum, a place where the Cowled Wizards keep their prisoners. He is put there because of his want for world domination as it would cause destruction if he tried. He cannot be recruited.

In-game biography
"When asked about his past, Tiax ignores you entirely, preferring instead to loudly proclaim what is in store for his future. He obviously worships Cyric, but also seems to share a touch of his madness. Tiax unquestioningly believes that he is destined to rule the world, and his fervor makes him blind to the ridiculous nature of the goal. He seems harmless for now."

Quotes

 * "The day will come when TIAX will point and click!"
 * "Tiax is as Tiax does."