Gilthanas is the second son of the Speaker of the sun. He doesn't stand the idea of seeing his sister with a bastard half-elven. As a child, he was in good terms with Tanis, but when Laurana started to stand around him too much, he lost his friendship. Later in the war of the Lance, Gilthanas and Tanis will make peace, and Tanis will finally marry Laurana.
Gilthanas is an apprentice mage. He only knows a few tricks, and isn't really serious about magic. He prefers fighting with a sharp sword or a good bow.
One day the companions will meet a young elf, Silvara, and Gilth will fall in love with her. The young elf will turn out to be a Silver Dragon, the sister of the Silver Dragon who fell in love with the great Huma. Gilthanas and Silvara will disappear from the story at a certain point.