In the early development, Kristoff was originally Kai as in Hans Christian Andersen's "The Snow Queen", but later he was designed as combination of Kai and the robber girl.
Voice
He is primarily voiced by Jonathan Groff, while he's voiced as a child by Tyree Brown.
Physical appearance
Kristoff is tall, rugged, handsome, and in his early twenties. His build is a distinct variation on most Disney heroes. He has broad shoulders, large hands and feet, and a muscular build. He is significantly larger than Princess Anna. His build is a realistic consequence of his rough life as a mountain-dwelling ice harvester.
Appearance
''Frozen''
Kristoff is the first major character to appear in the movie, and is introduced in "Frozen Heart", as an eight-year-old orphan boy with his baby reindeer, Sven, who becomes his best friend. He attempts to mimic the elder ice harvesters, with mixed success. Later that night, Sven is pulling him through the woods when the two horses belonging to the royal family of Arendelle ride past him at speed while transporting Anna to the trolls. Kristoff becomes intrigued as one of them is leaving behind a trail of ice. From a distance, Kristoff watches as Pabbie, leader of the trolls, heals Anna's head. At the same time, one of the female trolls Bulda adopts Kristoff as her own child. 13 years later, Kristoff is a seasoned ice harvester by trade who lives in the mountains near Arendelle. He is briefly seen in Arendelle selling ice while the camera tracks through Arendelle prior to Elsa's coronation. A few days after Elsa's eternal winter begins, Anna shows up at Wandering Oaken's Trading Post & Sauna in search of winter clothing. Kristoff arrives at the same time as her, covered in snow, seeking to purchase carrots for Sven and climbing rope. From Kristoff's exchange with Oaken, Anna hears that the blizzard in Arendelle comes from the North Mountain and assumes that is where Elsa is hiding. However, Kristoff is thrown out of the store for calling Oaken a crook. Seeing that Kristoff has a sled, Anna buys all of his items and urges him to take her to the North Mountain. Kristoff is reluctant to help her at first but eventually gives in. As Anna and Kristoff head for the North Mountain, Kristoff is incredulous learning about her whirlwind engagement to Hans. The conversation is cut short when their sled is attacked by hungry wolves. Although Anna, Kristoff and Sven escape by jumping over a chasm, the sled falls to the bottom of the ravine and explodes. He questions whether or not to continue helping Anna, agreeing once Anna promises to have his sled replaced. The next day, they meet Olaf, an anthropomorphic snowman unknowingly created by Elsa, who leads them the rest of the way to Elsa's ice castle. Kristoff waits outside while Anna tries to persuade Elsa to go back to Arendelle in order to put an end to the winter inadvertently created by Elsa but fails, and accidentally gets hit in the heart. Kristoff manages to rush Anna to Pabbie, but Pabbie says only "an act of true love" can save her. Thinking it is a "true love's kiss" from Hans, they head back to Arendelle. At the castle gate, he sadly hands Anna over to Hans. On the way back into the mountains, Sven attempts to push him back to Arendelle, but he refuses, thinking it is selfish to fulfill his love instead of letting Anna be saved by Hans. However, a giant snowstorm appears over Arendelle, prompting him to return. There he eventually finds Anna, but then he has to watch Anna freeze solid as she chooses to sacrifice herself, saving Elsa from being killed by Hans. Moments later Anna revives, as self-sacrifice counts as "an act of true love" which he is overjoyed by. In the end, he gets a new sled from Anna, and the two share a kiss.
''Frozen Fever''
In the short film Frozen Fever, Kristoff helps Elsa plan a surprise birthday party for Anna. While taking Anna on a birthday treasure hunt throughout the kingdom, Elsa comes down with a cold and unknowingly creates little snowmen called "snowgies" with each sneeze, which create trouble for Kristoff, Sven, and Olaf. Kristoff and Olaf later take the snowgies up to Elsa's ice palace to live with Marshmallow.
''Olaf's Frozen Adventure''
Kristoff appeared in a 21-minute holiday film along with Anna, Elsa, Olaf, and Sven, which debuted in theaters for a limited time engagement with Disney·Pixar's Coco on November 22, 2017. It made its television debut on ABC on December 14, 2017. Like the rest of Arendelle, it is revealed that Kristoff has his own holiday tradition, this being an annual celebration honoring Flemmingrad, a jolly fungus troll that was tragically killed by humans.
''Frozen II''
In the 2019 movie, Kristoff plans on proposing to Anna but is always too scared to ask her, but when Kristoff almost proposes, Anna is too distracted in finding and helping Elsa. During a ride on the sled, Kristoff tries to propose to Anna again when Elsa and Olaf are asleep but his plan backfires when he tries to explain their relationship. However, once Anna is reunited with Elsa and Olaf is brought back, Kristoff finally works up the courage to ask Anna to marry him in a simpler way than previous attempts and she happily accepts.
Disney theme parks
From July 5 to September 1, 2014, as part of 'Frozen' Summer Fun show at Disney's Hollywood Studios, Anna and Elsa appeared in a horse-drawn sleigh making their way down Hollywood Boulevard, alongside Kristoff and skaters, skiers and ice cutters in the Anna and Elsa's Royal Welcome section. The sisters will also make appearances in , where they are joined by royal historians to retell the history of Arendelle; and "Frozen" Fireworks Spectacular alongside Kristoff and Olaf, a fireworks display set to the music of Frozen. Officially starting January 7, 2014, Kristoff began making appearances alongside Anna and Elsa at Disney California Adventure in "For the First Time in Forever – A Frozen Sing-Along Celebration" in Hollywood Land as part of the park's "Frozen Fun" event.
Reception
Collider writer Matt Goldberg commented that Kristoff was "slightly less interesting than his love-interest ", but the cuteness of Anna and Kristoff’s relationship compensates the defect.
