Niju was impressively built, being the second largest (Nuk being larger due to his massive appetite) and almost certainly being the strongest member of the wolf pack which allowed him to intimidate and defeat other wolves, easily tackling and overpowering Aleu and throwing off Nava. His fur was brown with a gray underbelly. His only markings were dark patches around his eyes. In the film, his whiskers were purposely made more noticeable.
Unlike the elderly leader Nava, Niju was a very militant and arrogant wolf, fully willing to break the rules of the land and steal for what he desired, though seemingly doing so because of the desire to live. He was also shown to suffer from a fear of change (cainotophobia) which probably caused his cruel actions as Nava claimed that Niju would willingly starve or die than leave his homeland. He's led by fear rather than greed, though. And he was also known as negative, intelligent, judgmental, uncompromising, narcissistic, ill-tempered, jealous and unkind.
(If certain characters aren't here, that means that they've not had any thoughts about them nor interacted with them. Feel free to summarize their perspective. (Fanfictions NOT included))
Unlike Nava, he was hostile towards them when he first saw them, once Nava wanted to promote Balto to lead he would be angered as he is the beta of the pack (second-in-command). When the time was almost up, he tried to get as much members to go against Nava's plans but Balto would try to stop them but when the time was up, Niju would get Jealous the Balto is leading and attacks her duaghter for it, Nava tries to help her but his age prevents to do it. When Balto swim back, he wanted to fight but the pack's time was running out and Balto tells that if he wants to lead then do now. Niju would tell him that it's to dangerous and he'll end up fleeing the scene.
Unlike Nava, he was hostile towards them when he first saw them, when he heard that Nava is letting Balto to lead, he'll be hostile towards her as she was his daughter. When he tried to gain the lead to the pack, he'll be interrupted claims that she saw the future and wants the pack to be aware that the time is almost up. When Balto is leaving with the pack, he'll attack Aleu due to him being jealous, Nava tries to defend her but his age made him impossible to do so and they were both unmatched by him. Shortly after, Balto swims back, he wanted to fight as what he saw him doing to his daughter and almost drowning her but the pack's time was running out and Balto tells that if he wants to lead then do now as time was running out. Niju would tell him that it's to dangerous and he'll end up fleeing the scene.
Niju would be angered that Balto is gonna lead the pack despite him being the beta, much sooner, he'll try to gain the leadership by convincing them that Nava is leading them to their doom. He'll be interrupted claims that Aleu can see the future and wants the pack to be aware that the time is almost up. When Balto is leaving with the pack, he'll attack Aleu due to him being jealous of Balto being the leader, Nava tries to defend her but his age made him impossible to do so. When Balto swim back, he wanted to fight him but the pack's time was running out and Balto tells that if he wants to lead then do now. Niju would tell him that it's to dangerous and he'll end up fleeing the scene. Nava would find after this.
They would listen and follow his orders without reason, but they would all abandon him so they can go to the new leader.
Niju saw Balto and Aleu and ordered his followers to attack them, when he sees that they're not doing well, he tries to interfere but he'll be stop by Nava and the pack. He planned to take over the wolf pack with the aid of his followers, Nuk, Yak, and Sumac. Niju would convinced everyone that Nava would lead them to their doom, by that he'll gain a bunch of followers and eventually the wolf pack started to turn towards Niju and started to follow him, but Balto would try to stop them was outnumbered. When he almost reaches Nava, Aleu claims that she saw the future and the ice bridge will form when the ice bridge that led to the caribou formed, the entire pack including Nuk, Yak, and Sumac turned back to Nava, Balto and Aleu. Niju also attempted to kill the pack leader Nava who couldn't defend himself due to his age as well as Aleu as she tries to help him, but his plans were foiled by Balto. When Niju was given the opportunity to lead the pack, his "fear Of change" got the better of him and he fled into the forest. Nava claimed to Balto after they were off the ice that he would go and find Niju and that "one would not be whole without the other."