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 to his intended bride). After his 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, even striking Pocahontas 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.
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 friend Namontack up in a tree and shoots him in the leg, but just as a settler known as Ben is about to fatally strike 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 ask 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 he becomes consumed by jealousy, and attacks John Smith. As Pocahontas tries to break up the fight and John successfully begins to push the angry Kocoum off him, Thomas, a fellow 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, but only ends up breaking it as he falls into the water, lifeless.
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 her father so much that he calls off John's execution and the war itself.