Sven is a large tan caribou. He wears a red harness around his body. Around his neck, back and hooves, he has tufts of white fur in a dusty pattern. The top of his head is a copper-brown color, unlike the rest of his body. If one looks closely, it is shown that he has brown eyes.
A Boy and his Reindeer
As juveniles, Kristoff and Sven spent their time with the ice harvesters, learning the ways of the profession and tagging along whenever they can. One night, Kristoff and Sven notice the royal family (the king, queen, Princess Elsa, and Princess Anna), rushing over to the Valley of the Living Rock. Curious, the boy and reindeer follow behind to watch what all the commotion is about. As they spied, they're discovered by one of the trolls, Bulda, who decides to adopt the two orphans. From there, Kristoff and Sven became family with the trolls, officially taking residence in their valley. Years later, Princess Elsa is set to become queen after the death of the original monarchs, and whilst the kingdom is abuzz with royals from all around, Kristoff and Sven are out and about, too, but don't attend the castle festivities, likely because it's meant for royalty only.
Later that night, Queen Elsa was revealed to have great power over ice and snow, and as she flees her kingdom due to being called a monster, she accidentally curses the kingdom, causing an eternal winter in the process, and just as Kristoff and Sven were making their way to the North Mountain. The next night, Kristoff was busy buying equipment for his travels, as well as carrots for Sven, from Wandering Oaken's Trading Post and Sauna, but gets kicked our for calling the store owner a crook, much to Sven's disappointment. They decide to sleep in a stable for the night, and as they sing their lullaby "duet," with Kristoff singing his reserved lyrics in a different voice, Princess Anna pays them a visit and asks Kristoff to guide her to the northern mountains to find her sister. Kristoff denies until Anna shows she has purchased the equipment and carrots he failed to buy. Sven is more than happy to help at that point, and the trio head off. After facing a wolf attack, however, Kristoff wants to call it quits, but Sven doesn't want to leave Anna out alone, knowing she'll die, and persuades Kristoff to continue forth.
A New Friend for Sven
Later on, they meet an enchanted snowman named Olaf, brought to life by Elsa, who offers to guide them to her ice palace. Sven immediately takes a liking to the goofy snowman, and the two form a bond. But Sven also takes a liking to Olaf's carrot nose, which he tries to eat a few times, with no success. Soon enough, the friends find Elsa's palace, but he's unable to make it up the ice stairs. Kristoff tells Sven to wait outside, and when the others return, they are being chased by a giant snow monster. Kristoff, Olaf, and Anna head off, and Sven goes in a different direction, meeting up with the gang at the bottom of a mountain cliff. At that time, Kristoff realizes Anna's been cursed when Elsa accidentally blasted her with magic back at the castle, and he leads the way to the Valley of the Living Rock.
Return to Arendelle
Pabbie, the king of the trolls, tells the group that unless Anna performs or recives an act of true love, she'll freeze to death. Riding on Sven, the group rushes back to Arendelle for Anna to kiss Hans, her fiancé, believing true love's kiss would break the curse. Once they arrive at the castle and the princess is taken into royal care, Kristoff reluctantly takes his leave despite his romantic feelings for Anna, believing they could never be as Hans is apparently her true love. Sadly, the mountain man heads back into the mountains with Sven trudging along, only to eventually halt in his tracks, look back at the kingdom, and realize leaving Anna without Kristoff confessing his true feelings isn't right. The reindeer rushes in front of the ice harvester and tries to convince him to head back, but Kristoff angrily denies, telling Sven going back would be pointless as Anna's with her true love. However, seconds after, a gust of frosty wind hits the duo, and looking back at the castle, they see the kingdom being consumed by a deadly blizzard. Knowing Anna must be in danger, Sven and Kristoff rush back to Arendelle to her rescue.
Rushing back to the castle, the blizzard becomes much more powerful, though it only prompts Sven to increase his speed, as the reindeer is highly devoted to getting Kristoff to his true love. From the castle library, Olaf and Anna are able to spot Kristoff and Sven rushing to them in the distance, having the duo head out into the frozen fjords to meet them. During the chaos, Olaf is separated from the princess, and likewise, a ship causes the icy ground beneath Sven to crack, unleashing freezing waters. Sven tries to avoid them, but only manages to get Kristoff to safety before falling head-first into the freezing waters, apparently drowning, much to Kristoff's horror. However, Sven luckily survives and pulls himself onto a drifting iceberg, telling Kristoff to keep moving without him, which the mountain man obliges to.
When he reunites with the others, Sven finds Anna frozen solid, having sacrificed herself to save Elsa from the treacherous Hans. Fortunately, that's an act of true love, and Anna is reborn. The rest of the kingdom is thawed, as well, and Elsa reclaims her throne. As a reward, Sven is appointed royalty by Elsa, and welcomed into the castle as such along with Kristoff and Olaf, who is given his own snow cloud to survive in summer. As the snowman enjoys the season, he sneezes, his carrot nose flying right into Sven's mouth. Sven playfully sucks it in, much to Olaf's sadness, but immediately places it back onto the snowman's face, proclaiming their friendship. Sven is last seen with Olaf, Kristoff, Anna, and Elsa skating in the new ice skating rink of the castle's courtyard, enjoying the peace and freedom Arendelle greatly longed for.
In the promotional trailer when Olaf meets him, Sven and him start slipping on ice. Sven tries to eat Olaf's nose, but he puts it back. To avoid losing his nose as he smells his hair, Olaf covers it. Olaf's head is blasted in the air.
When playing hockey, he is seen with Kristoff in a black screen. The puck is hit, breaking the screen.