She had a spellscar that made her magic much more powerful than it would otherwise be. However, her magic often ran wild and she had a difficult time controlling the effects of her spells. Additionally, every time she used magic, it took a huge emotional and physical toll.
Her birth mother was a wizard and she inherited some of her mother's magical ability. Icelin's parents were scholars from Baldur's Gate who were adventuring partners with a gold elf named Cerest Elenithil and a human named Elgreth. They often took her along on expeditions to study the effects of the Spellplague. On one of their expeditions, her parents accidentally released dormant blue fire, which killed them and left Icelin, Elgreth, and Cerest spellscared.
Elgreth's spellscar gave him the power to detect magic, an extremely useful skill for a treasure hunter. He was concerned that Cerest believed Icelin had the same ability and would attempt to use Icelin's power, so he took Icelin to live with his brother, Brant, in Waterdeep's South Ward.
Icelin grew up in Brant's dry goods shop. She received training in the arts from a local wizard and became a very powerful mage for her age although she had difficulty controlling her magic. Icelin accidentally burned down a boarding house, killing several people, when a spell went wild. She helped to support herself and Brant by performing magical services for pay.
One afternoon, Icelin ran into Cerest completely by chance in the South Ward. She saved his life by pushing him out of the way of a spooked horse. Cerest recognized her and when Icelin wasn't willing to accompany him back to his home, his men killed Brant and framed Icelin for the murder. Cerest convinced the City Watch that Icelin was responsible for the murder and the Watch attempted to apprehend Icelin.
Icelin fled with Sull the butcher to Mistshore in an attempt to hide from the Watch and Cerest. In Mistshore, she hired the services of a monk name Ruen Morleth to hide her from Cerest. Cerest captured Icelin briefly but she was able to escape with the help of Sull and Ruen. She hid for a time in the hideout of a local crime lord and had a final showdown with Cerest on an old wrecked ship in Waterdeep's harbor.
Icelin called upon the blue fire within her and in the wreck to kill Cerest. The effects of the blue fire aged her and she thereafter looked and felt like a middle-aged woman. Icelin was later exonerated by the Watch for Brant's murder and left Waterdeep with Ruen and Sull on a journey to find a cure for her spellscar.
Icelin was short and thin with black hair and pale skin. She looked much older than her true age due to the effects of wild magic.