Sven is the loyal pet reindeer and companion of Kristoff, a rugged mountain man. Together, the duo run an ice harvesting business (which has greatly enhanced Sven's overall strength, making him quite the force) and reside outside the city of Arendelle in the Valley of the Living Rock, where a community of trolls thrive. The trolls adopted both Kristoff and Sven when they were children, and raised them. Also, according to Frozen: The Essential Guide, Sven was rescued by Kristoff as a young fawn, and remained by his side ever since. Though Sven cannot speak, Kristoff has come to fully understand the reindeer merely through the latter's actions and expressions, to the point where he does his own (surprisingly accurate) voice-overs for Sven.
Personality
Sven in the Frozen teaser.
Sven is goofy, loyal and rather childish. He spends most of the film by Kristoff's side, acting as his closest friend (even in their younger years) and conscience. And while Sven may not seem incredibly intelligent, he does have a strong moral character. Throughout the film, he constantly convinces Kristoff to do the right thing, including assisting Anna in her journey to find Elsa, and later returning to Arendelle to confess his love for the princess after their adventure comes to a conclusion. Along with Kristoff, Sven also seems to be greatly close to Olaf, enjoying the snowman's antics and eventually creating a close bond throughout the course of the film. As a running gag, however, Sven tries to grab a bite of Olaf's carrot nose. In the end of the film, he manages to do just that, but immediately returns it, showing he was merely being playful with his newfound friend, much to Olaf's delight.
Key to his character, Sven lacks qualities of an actual reindeer, aside from appearance and vocal affects. Instead, he's shown to have the personality of a dog, as he's constantly seen panting (though reindeer tend to do this, as well), wagging his tail, and performing the "play bow" stance, which dogs tend to use as a way to initiate playtime.
Physical Appearance
Sven is a large, tan reindeer with brown eyes. 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.
Trivia
Concept Art.
Sven was originally set to be a one-antlered reindeer.
His favorite snacks are carrots.
The Frozen filmmakers invited a real-life reindeer into the Walt Disney Animation Studios, observing the animal's physical makeup and mannerism, which were later caricatured in the design of Sven. This process was done before, involving a rabbit and two fawns for the film Bambi.
Whilst the filmmakers have noted Sven's behavior being based off that of a dog (or a Labrador to be more precise), real reindeer actually do pant much like canines. Real reindeer also scratch the back of their ears with their legs, much like dogs, and that was also incorporated into Sven's character.
Sven is also similar to Pegasus from Hercules and Maximus from Tangled in a way that they are animal sidekicks to the protagonist, and act like a dog.
Sven resembles Rutt and Tuke the moose from Brother Bear, which is ironic since in Europe, moose are known as "elk". In North America, elk or wapiti are an entirely different animal altogether.
For an animal that is not a horse, Sven is an incredibly fast reindeer (even as a calf), which is actually a big reference to his species, as reindeer are fast enough for Eskimos and many other cultures to use them in sled races in the Northern hemisphere.
Sven is also shown to be very strong. After he threw Kristoff across the ice and sank, he swam all the way to the top.
Sven has the antlers of a female reindeer.
As Olaf symbolizes Anna and Elsa's bond, Sven symbolizes the bond between Anna and Kristoff.
And based on Olaf and Sven's close friendship in the movie, it is likely that Kristoff and Elsa became good friends too.
Sven was originally going to be known as "Thor", after the Norse god of thunder, but was changed to avoid confusion with the Marvel superhero of the same name.
It's possible that Sven, along with Hans, Kristoff and Anna, is named after Hans Christian Andersen, the author of The Snow Queen and also The Little Mermaid.
The Frozen creators were eager enough to bring in a real reindeer in order to capture the appearance and behavior of Sven. In the end, it didn't work out, as they found real reindeer quite boring. Instead, they brought in one of the directors' dogs called Frankie, and Sven's personality turned out to be more lively.
