Nuka is the oldest son of Zira and was born at some point during Scar's reign as King of the Pride Lands.Sometime in between the events of The Lion King and The Lion King II: Simba's Pride, he was banished to the Outlands alongside Zira, his siblings and the rest of Scar's followers. Despite being the oldest of Zira's children, he is neglected by Zira in favor of Kovu, Scar's chosen heir.
Nuka is shown to be cowardly, somewhat slightly neurotic. However, he has an inflated opinion of himself, as he claims to be the strongest and the smartest. Considering his feelings of inadequacy and bitterness over his pride's favoritism towards Kovu, however, it is likely his egotism is, in fact, a defense mechanism to shield his insecurities and grant himself a sense of self-worth. Because he is neglected by Zira in favor of Kovu, Nuka is shown to have a strong dislike and envious sibling rivalry for his younger brother. Nuka also desires to please his mother, in order to get her attention, which eventually leads to his downfall. This makes him somewhat of a tragic figure and a complex character as he is motivated by a longing for the praise and love Kovu receives from Zira more than anything else.
In addition, it is also implied that he has some mental and emotional instability, including pyromania, as evidenced by when, before proceeding to burn a large part of the Pride Lands to trick Simba into allowing Kovu into the pride as part of Zira's plan, he shouts "Woo! Fire!" Nuka also has a sarcastic side, sarcastically calling Kovu "The Chosen One" when out of sight, and a wicked side to him cutting a branch Vitani is pulling only to give a wicked laugh when she falls backward. At the end, Nuka gets the courage to go after Simba himself, but it costs him his life.
Nuka is extremely mangy and is apparently infested with termites (partly due to living in a termite mound). Nuka has brown fur and a black mane and keeps his front claws unsheathed, a trait seen in all the Outsiders. Judging from the thickness of his mane in his first appearance, he would be about a year and a half old. Despite being older than Kovu, his mane does not grow in as thickly - a trait seen in real lions, where stronger lions usually have thicker, fuller manes.
In the film, Nuka is shown as a teenager at the home of the Outsiders, arguing with his younger sister, Vitani, over Kovu. Nuka has apparently left Kovu alone, despite being asked to babysit him, and it is implied that this happens often. Nuka expresses his jealousy over Kovu's position as Scar's chosen heir, as he was passed over despite being the oldest of Zira's children. He states his intention to tell his mother that he should be the heir, but quickly backs down after Zira returns and scolds him for not watching Kovu. Nuka watches as Zira makes a plan to have Kovu get close to Kiara so that Kovu can eventually kill Simba. When Zira lavishes a praising comparison of Kovu to Scar to the cub for his supposed brilliance Nuka groans in disgust only to be silenced by a growl from Zira and mutters bitterly, "Chosen one", as the two make their leave. Though Nuka likes the idea of killing Simba, he shows displeasure when Kovu's part in the plot is mentioned.
Nuka's next major appearance is as an adult, wandering the elephant graveyard with Vitani. The two have been tasked with setting a wildfire while Simba's daughter, Kiara, is out on her first hunt. He expresses revulsion at their surroundings denying Vitani's dismissal of his repulsion as fear. He is shown to continue to resent Kovu's position as an heir and his mother's favoritism towards him. Zira's plot is to have Kovu rescue Kiara from the fire, to allow Kovu to get close to Simba and kill him. The plan is successful, as Kovu saves Kiara from the wildfire, and is allowed to return to the Pride Lands. Nuka secretly follows the pride alongside his mother, in order to spy on Kovu. Whilst the two are watching Kovu's conversation with Kiara, Nuka furiously reacts when he makes no attempt to kill her but his mother hushes his protests noting that with Kovu and Kiara growing closer their goal of Simba's death is close to being reached.
When it appears that Kovu is beginning to have second thoughts about his role in Zira's plot, Nuka accompanies the Outsiders as part of an ambush, to try to kill Simba. As Zira orders the attack, Nuka is the first to tackle Simba, yet is swatted away. Simba is then cornered in a ravine and is forced to climb a log dam to escape. When Kovu refuses Zira's order to kill Simba, Nuka impulsively decides to do it himself, exclaiming, "I'll do it - for you, Mother! Mother, are you watching?! I'm doing it for you... and I'm doing it for me!"
However, while briefly grabbing Simba's ankle, Nuka slips and falls, ending up being crushed under several logs. Kovu rushes forward to dig him out but is knocked aside by the frantic Zira, who finishes the job herself. Nuka succumbs to his injuries, after apologizing to his mother for his failure. Ironically, through his death, he finally gains his mother's attention and affection, and Zira blames Kovu for Nuka's death by slashing him across the face, which leaves him with a scar on his face.
The film draws parallels between the relationships of Scar and Mufasa and Nuka and Kovu. Scar became jealous of Mufasa's kingship and Simba's potential passage to the throne, which left him out of the direct succession. Nuka has similar feelings towards Kovu, but as he is less intelligent and more cowardly than Scar was, and also because he desires to gain his mother's approval, his jealousy comes across as more 'goofy' than evil.
In an original cut of the film, Nuka's death scene is extended. After Nuka, being crushed in the logs, says "I'm sorry, Mother. I tried." Zira manages to reach her paw to cradle his head gently. Pleased with Zira's affection towards him, Nuka says "Well, I finally got your attention, didn't I?" before he finally dies. Zira then asks Scar to watch over Nuka.
Nuka along with Kovu, Vitani, Zira and their pride appear in the Disney Junior series The Lion Guard episode "Lions of the Outlands". He is first seen pouncing on Jasiri telling her to stay away from the watering hole only to bested by Kion. When Zira makes Kion use the Roar to create rain he watches in slight awe and fear. Later he tries to "hunt" Jasiri only to be humiliated as she easily avoids him. Nuka only shows the confidence to attack Kion again, when he's surrounded by the others in his pride and told Kion can't use the Roar on other lions. Once again Kion easily beats him. He is last scene being blasted out of the Outlands to the termite mounds.
- In some Simba's Pride books, Nuka is referred to as Zira's second-in-command. It is unclear whether this is true or not as the spot seems to belong to Vitani in the second half of the film.
- He can still be heard saying, "Didn't I?" during the finalized film, possibly apart from the deleted scene the editors forgot to cut out. It, however, is colored and could be intentional. It is often mistaken for a groan of pain.
- Nuka's mane swaps between black and dark brown frequently throughout the film while his beard and elbow tufts stay black. His mane remains primarily black, though.
- Nuka is the only Outsider who wants to kill King Simba for reasons not applying to avenge Scar's death.
- Since The Lion King II: Simba's Pride is adapted from Romeo & Juliet, Nuka is most likely based on Tybalt in that he is Kovu's rival, the same way Tybalt is Romeo's, and their deaths heightened the tensions in their respective stories. The only difference is that Tybalt and Romeo were members of two opposing factions (the Capulets and the Montagues, respectively) while Nuka and Kovu were actually part of the same faction (the Outsiders) and technically brothers.
- Zira appears to love him as well as Kovu and Vitani but was too focused on Kovu becoming Simba's murderer that she paid too less attention to him.
- In an earlier draft of the movie, Nuka was supposed to be a serious villain rather than the comic relief he was in the final movie.
- Zira and Nuka are the only two villains in the film who are not redeemed.
- Despite being listed as enemies with Nala and Kiara, Nuka doesn't interact with either one of them in the film at all.
- Despite his resentment towards Kovu in The Lion King II, they appear to have a decent relationship in The Lion Guard.