Kocoum is Chief Powhatan's strongest warrior and fought bravely in the battle against the Massawomecks. He considered to be handsome by many. He is described as being serious, and rarely smiles (not even at Pocahontas). After showing his courage during a war, he effectively becomes Powhatan's second in command. He appears to genuinely love Pocahontas despite his seriousness, but when he sees she loves John Smith, he is consumed by jealousy and attacks John instead of trying to use the situation to encourage peace, and tries to murder him, while even pushing Pocahontas away in the process. Kocoum also cares about his friends and people. When one of his friends is injured in a fight with the settlers, Kocoum immediately rushes to his aid and watches over him as he is being treated.
Kocoum is first seen when Pocahontas returns to the village. Chief Powhatan is telling the people of his courage during the recent fight against the Massawomecks. Powhatan tells that Kocoum had fought with the strength of a bear, with bear paws being painted on his chest to symbolize this. Finally, Powhatan calls for a feast in Kocoum's honor.
It is later discovered during a conversation between Pocahontas and Powhatan that Kocoum has asked to seek Pocahontas's hand in marriage. Pocahontas believes that Kocoum is just too serious for her, but her father tells her that Kocoum will make a fine husband because he is loyal and strong. According to Powhatan, Kocoum would also build Pocahontas a good house with sturdy walls where she (and their many possible children in his unspoken words) would be safe from harm. While this is true, Pocahontas tries to explain to her father that the dream she had showed her a different path.
When the settlers arrive, Kocoum offers to lead the warriors to the river and attack them, with the intention of destroying them the way they destroyed the Massawomecks. Chief Powhatan points out that they know little about the white men, and merely orders Kocoum to take some men to the river to observe them.
When Kocoum arrives at the river they see the settlers digging up for gold. Kocoum is able to determine that the settlers number more than 100. However, Governor Ratcliffe spots the scouts and orders an attack, assuming it is an ambush. He spots Kocoum's best friend Namontack up in a tree and shoots him in the leg, but just as a settler known as Ben is about to pistol-whip Namontack, Kocoum bursts in and pushes him out of the way, picks Namontack up, and orders a retreat.
When Chief Powahatan hears of this, he orders nobody to approach the white men (not knowing that his daughter has already met one). He asks Kocoum to send messengers to neighboring villages to ask for aid in fighting the settlers. The next day, Powhatan sends for Kocoum to watch over Pocahontas and her friend Nakoma while they gather food for when the warriors arrive but when Kocoum shows up only Nakoma is there. She tells Kocoum that she hasn't seen Pocahontas (who snuck off with John Smith into the woods). Kocoum tells Nakoma to tell Pocahontas that she can't keep running off because it's dangerous out there. When the warriors arrive and Pocahontas comes back from being in the woods, Kocoum approaches her and tells her that they are going to fight the settlers, calling them "white demons", and putting his arm around her shoulder. This is the only time in the final cut of the film that they actually speak to each other, and the only time that Kocoum shows a gesture of affection to her.
That night, Pocahontas goes to the woods to meet John Smith, and Nakoma tells Kocoum, believing Pocahontas is getting herself into trouble. When Kocoum spots John Smith and Pocahontas together kissing in Grandmother Willow's glade, he is overwhelmed with jealousy, and proceeds to attack John Smith in an attempt to murder him out of fear that he'll hurt Pocahontas. As Pocahontas tries to break up the fight and John successfully begins to push the angry Kocoum off him, Thomas, a fellow soldier and settler who had been ordered to follow Smith, intervenes and kills Kocoum with a single gunshot. As he dies, Kocoum attempts to hold onto Pocahontas by the necklace and breaks it. Pocahontas mourns him upon seeing him with a bullet hole in his chest.
When Kocoum's body is brought back to the village, the warriors tell the Chief that Kocoum went to find Pocahontas out in the woods and that John Smith attacked him. Powhatan blames Pocahontas' actions as leading to Kocoum's death and believes that John Smith killed Kocoum. Kocoum's death very nearly serves as the catalyst for an all-out war between the settlers and the Powhatans, but Pocahontas' wisdom moves him. Chief Powhatan realizes that Kocoum would not have wanted a war and calls off John's execution and declares that war is not the answer.
Although Kocoum does not appear in the sequel, Nakoma's husband bears a close resemblance to him.
- In the deleted scene "Dancing to the Wedding Drum", Kocoum displayed a different personality than the one that he would get in the final version of the film. He actually showed his love for Pocahontas by speaking very kindly to her, he smiled more and their home, which he built, was already completed. He even sings to her in the scene.
- Unlike Gaston's affection towards Belle in Beauty and the Beast, Kocoum cared about Pocahontas for more than just her looks and was not vain, but it was his stern and bitter demeanor that put Pocahontas off him, while Gaston became his film's primary antagonist.
- The real Pocahontas married Kocoum three years before Englishmen captured her in northern Virginia. They were led by the sea captain, Samuel Argall with assistance from Kocoum's older brother, Japazaws. Her father's tribe stole weapons and agricultural tools from the colonists. In addition to that, her father kept English prisoners. After these prisoners were set free, Pocahontas remained hostage under Sir Thomas Dale in the settlement of Henricus.
- In real life, Kocoum was slain by Captain Argall's soldiers when Pocahontas had her abduction on April 13, 1613. He was survived by his daughter, Ka-Okee. She resided with her father's tribe after this incident, but never saw her mother again.
- Kocoum's death was foreshadowed during Kekata's vision that a "pack of wolves" (representing the settlers) appearing from smoke will threaten to attack the Powhatans' tribe, and the smoke wolves starts swirling around Kocoum.
- According to information, there may not have been a man named Kocoum. It is suggested to have been in fact a nickname for Rolfe himself, with the reference being later misunderstood as one of Powhatan's officers. This is supported by the fact there's no hint of her ever being married before John Rolfe.