Tanis was born from an elven mother and a human rapist. He was adopted by the Speaker of the Sun. The elven Princess Laurana soon fell in love with him, but she was still a kid. Besides, he, because of his human half, grew faster then his elven cousins. He never really felt home in Qualinesti.
Then Flint Fireforge, and old dwarven blacksmith, came to Qualinesti. Tanis decided to follow him back to Solace, Flint's home. This is where they met the other companions of the lance; Tassleoff Burfoot, Caramon and Raistlin Majere, Sturm Brightblade, and Kitiara Uth Matar...Kit....
Tanis fell in love with Kitiara, a human mercenary. They were as alike as fire and water, but he sincerely loved her. Then the companions separated for five years to seek for the real gods. When they came back, everybody was there, except for Kitiara, and that broke Tanis's heart.
Anyway he is the leader of the companion, even if he hasn't anything very special, unless maybe a deep friendship with his companions. He didn't chose to be the leader; only the other companions would trust him with the eyes closed. He then lead the companions to the War of the Lance, in which he played a key role: he killed the Dragon Highlord Ariakas (with some help from Raistlin tough). After that he got married with Laurana.
He made his way to the Chaos War, where he was killed by a barbarian, as he just saved Steel Brightblade Uth Matar, the son of Sturm and Kitiara.