Kris Dreemur is a human 18 year old. In the Light World they have amber skin tone and shoulder-length dark maroon hair with long bangs. They wear a long-sleeve lime shirt with one horizontal yellow stripe, and nondescript pants and shoes. One of Kris's distinct traits is that their long bangs cast a shadow that hides their eyes. In the brief moments they tear the SOUL out of their body, their red eyes can glow in the dark. One of their crimson eyes is also visible for a few frames when they descend into a Dark World. Kris is grumpy and tired and usually crude (usually saying words like fuckin', callin', sleepin' etc) despite being flirtatious at times. They are quite creepy sometimes due to their lack of social skills. Kris is adopted by two anthropomorphic goats, Toriel and Asgore and has an adoptive brother which is Asriel. Kris is also friends with Susie, a tall purple anthropomorphic reptile.

During the events of Deltarune, Kris is mentioned to be an introvert. Susie and King refer to Kris as a "quiet person," and Noelle is astonished if they converse about "anything." After Kris's brother, Asriel, left for college, they became distant from their few friends. Kris's side of their shared bedroom is also strikingly bare. The shared game console is underneath Asriel's bed, and their old children's books are in Toriel 's classroom instead. Toriel has also mentioned that Kris is not normally energetic. They have a history of not waking up on time, and often slept through the start of class Kris also preferred their mother driving them to and from school than walking.

Contrary to Kris's apparent detachment, they do have a variety of interests. Kris has always been mischievous, pulling dark pranks such as covering themself in ketchup and claiming it was blood. For example, Kris has the option to keep flushing the toilet before or after going to school, with Toriel replying: "You did not put a bath bomb in the toilet again, did you?"

Kris enjoys playing the piano. Prior to the game, they frequently played the hospital piano, despite it "missing most of the good keys." They have searched for tutorials to improve, and Red Big Mouth believes they can play the hospital piano "beautifully." In a private post from Noelle's blog, Noelle mentions that Kris would often come to her house and use her piano since Kris did not have one in their home. Noelle explains that whenever she followed them into the dining room to listen to them play, Kris would immediately stop playing. Without an interruption from Noelle, however, Kris would continue playing, sometimes for hours at a time.

When younger, Kris studied the occult with Catti. They appear to still have an interest in this topic, as one of their search queries was "how to use magic."

At the end of Chapter 1, Red Big Mouth and Toriel both comment on Kris's physical appearance. They cite that Kris seems "a little sick" and does "not look quite yourself" respectively. It is implied that the SOUL is the reason, though the exact cause is unknown. Notably, Kris wants to be perceived as "normal" despite Toriel's concern.

Kris is shown to have a significant amount of agency outside of the player's choices when in the Light world. This is most clearly shown in scenes where Kris rips the SOUL out of their body, but also in how characters react to Kris's dialogue choices: occasionally, the player may choose an option that other characters note sounds like Kris is straining to say. Kris is also shown performing actions independently of the player's control, including protecting Susie from King or awkwardly trying to escape the Sweet Cap'n Cakes fight with Ralsei and Susie, showing their friendship with the two exists outside of the player's influence. Additionally, there are some instances in Chapter 2 where Kris stops inspecting something relating to their home life, preventing the player from learning more: when inspecting Asriel's room in Queen's Mansion, Kris closes their eyes before peeking into Asriel's room in the Guest Hall; when inspecting an article about Asgore's firing and Undyne's promotion, Kris intentionally stops reading before the reason is given. The separation between the player and Kris is most clearly shown in the Weird Route, where it is heavily implied Kris's actions are being done against their will. Noelle describes the voice she heard giving her orders as terrifying, noting Kris has been acting very strange lately. When Kris reunites with the party after defeating Berdly, Susie and Ralsei immediately notice Kris appears distraught.

Another instance of this happens in the normal route of Chapter 2, where after defeating Spamton NEO, Susie notices Kris appearing to be in shock. If the player responds to Susie that they're okay by saying Yes, Kris appears strained in their response, making Susie think that they're not okay; if the player responds to Susie by saying No, Kris yells out the response, concerning Susie and Ralsei. This heavily implies that Spamton's dialogues about being a puppet and cutting his strings to be free, combined with Spamton's ultimate fate, deeply unsettled Kris.

Years ago, Kris was adopted by the Dreemurrs and grew up in a loving family. However, as the only human child in Hometown, Kris often felt like an outsider. Kris once asked their adoptive parents when their "horns were going to grow in." In response, Toriel and Asgore bought a headband with red horns for Kris, who wore it for months.

Growing up, Kris became very close with their older brother, Asriel. The two often explored the forests around town with their neighbors, Dess and Noelle Holiday. While Kris went over to the Holiday residence and played with or pranked Noelle, they would go to play the piano but stop if Noelle was watching. The four were close friends, Kris and Noelle grew apart over the years. The cause for this is unknown but is implied to have been related to Dess subsequent disappearance. Kris had also wanted to befriend Bratty, as she was one of the "big kids." They willingly complied and retrieved food for her until she became sick.

At some point, Toriel and Asgore became divorced. It is implied in Chapter 3, that prior to the divorce Kris witnessed various arguments from their parents leaving them distressed. It is also heavily implied in the Egg segments that Kris went through some sort of traumatic event that they repress, given that interactions with the Man point to something they saw behind a tree that they cannot bring themself to fully see or draw out. While their family was broken, Kris and Asriel remained inseparable. On occasion, Asriel would buy Kris a hot chocolate at QC's Diner, something they used to do together as a whole family. One day, Asriel had to go away to college, leaving Kris alone and without many friends.