Role in the film
Sitka loves his younger brothers and would do anything for them, the movie begins Kenai's coming of age ceremony and receives an animal totem which represents their personalities and his happens to be a bear, which he hates because they steal food from them and Denahi teases him for it angering him. Later that night, Sitka tells him of his own ceremony and how his totem is the eagle, which represent leadership. The next day, they find that a bear has stolen some fish from them because Kenai didn't secure the ropes on the basket and he recklessly goes off to kill the bear. Sitka and Denahi follow him to make sure he doesn't end up getting killed.
Kenai is knocked to the ground and Denahi defends him, but the bear knocks the spear out of his hands and it looks like it's over for them when Sitka, deciding there is no other option, stabs the ice around the bear with his spear, causing the ice to crack and break, off causing the bear to fall and Sitka falls with her. Kenai and Denahi search for him, but only find his coat and his spirit assumes the form of a bald eagle. Later that night, a funeral is held for Sitka and Kenai is enraged that the bear lived and Sitka died and feels responsible for what happened, so he goes out to kill the bear to avenge Sitka. After a battle, he succeeds. Feeling that it wasn't necessary for Kenai to kill the bear, as Sitka willingly gave his life to protect them, Sitka's spirit decides to punish Kenai and turns him into a bear.
Thinking the bear killed Kenai, Denahi decides to avenge his death and tracks him down and Kenai escapes and has to look after the bear's cub, Koda, whom he finds annoying at first, but eventually grows to love him. At the end of the movie, upon seeing Kenai nearly give his life for Koda, Sitka decides to change him back into a human and visits him and Denahi in his human form before departing to the spirit world but, before he leaves, Kenai wishes to be a bear again so that he can look after Koda, because he can't talk to him in human form. Sitka was voiced by D.B. Sweeney who had previously voiced Aladar in Disney Dinosaur.
He does make a cameo in eagle form near the end in Brother Bear 2 with the spirits transforming Nita into a bear. Also, while Nita and Kenai are traveling, an eagle flies to a nest to bring some chicks food---implying that Sitka may have mated with a female eagle and become a parent.