Some actors look truly unrecognizable in films.
For certain movies, stars must undergo a physical transformation in order to present a believable portrayal of a character. This can include makeup, prosthetics, and even weight changes.
Here are the surprising celebrities behind some of Hollywood's most well-known villains, creatures, and monsters.
SEE ALSO: 36 celebrity best friends who met on set
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The 29-year-old Swedish actor made his debut as Pennywise in the 2017 horror movie "It," based on a Stephen King novel.
"It was an amazing, terrifying feeling of seeing the makeup go on for the first time," Skarsgard told Us Weekly in 2017.
"Up until that point, I didn't know what the character actually would look like," he continued. "So every step of the way, I was looking at myself in the mirror, making faces to try to see what this character would eventually be."
The child stars of "It" didn't even see Skarsgard in full costume until they filmed the protector scene, so when the clown appeared, the terrified reactions were genuine. Skarsgard also made some kids on the set cry.
Speaking to "Entertainment Tonight," Skarsgard said that he has a lazy eye, which enabled him to move the physical feature in a different direction.
As for Pennywise's horrific smile, the actor told Conan O'Brien that he learned to contort his lips in a "strange way" after seeing older brother Gustav Skarsgard do it. Around 10 years old, Gutav picked up the skill as well, made up an evil character, and purposely ran around scaring his younger sibling.
You can see practical effects artists Tom Woodruff Jr. and Alec Gillis break down how they created the Pennywise mask in this video shared by PopSugar.
The actress appeared on NBC's "Tonight Show Starring Jimmy Fallon" in 2014 and said that the time eventually got cut down to three hours. She also used to stand or sit on a bicycle to be painted.
For "X-Men: First Class," Lawrence got covered in head-to-toe body paint, which led to "weird boils, rashes, and blisters."
To avoid skin irritations for the "X-Men" sequels, Lawrence switched to a bodysuit from the neck down.
In a 2015 Marvel featurette, Bettany said that his face gets painted and then a rubber balaclava is put over his head and glued to his face. He also wears a "robot muscle suit" that's equipped with tubes that run ice water through to keep his body cool.
"It's pretty painful, it's uncomfortable," Bettany told USA Today in 2015.
Read more: 14 Marvel stars who shared the challenges of wearing superhero costumes
The fan-favorite character experienced a makeunder near the end of the franchise. But before that, she was introduced as an over-the-top District 12 adviser with an affinity for luxurious items.
Banks told MTV that getting all the components of the costume on her took two hours once they got the process figured out. She went on to say that her long Effie nails were the most problematic aspect because once they were on, she couldn't type on her phone, use a computer, or go to the bathroom. The actress also said that the lavish outfits were "constricting" and didn't allow for too much movement.
Speaking to People, Banks said that another difficulty was resisting the urge to touch her face while in full makeup. The elaborate eyelash details also took some time to get used to.
The actress went on to say that she passed time during the transformations by napping.
"I find it very soothing when people touch my face and hair," she said. "I also spent time reading, chatting and hanging out with other cast members. Since I was in there the longest, I usually got to see everyone arrive."
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Isaac, who played the titular villain in the 2016 movie, told GQ: "I didn't know when I said yes that that was what was going to be happening, that I was going to be encased in glue, latex, and a 40-pound suit — that I had to wear a cooling mechanism at all times."
He added: "I couldn't move my head, ever."
Isaac wore multiple head and face pieces and the bulky armor seen in the film was 3D-printed.
Speaking to Harper's Bazaar for the December 2018/January 2019 cover, Robbie said that she would start each day on set getting her head wrapped before a bald cap and wig were put on.
The actress also wore white powder and the shape of her eyebrows was altered.
"Surprisingly, the quick part was the white makeup," Robbie told Harper's Bazaar. "And the heavily drawn-on blush, eyebrows, lips."
In the film, Queen Elizabeth I had scars as a result of smallpox. In order to achieve a similar effect, Robbie wore fake scars that were created using prosthetics.
"With smallpox, you are left with a very badly scarred face, and your hair falling out, so I used that route to try and change Margot Robbie's features, by placing the boils of the smallpox along her bottom lip," Jenny Shircore, the movie's hair and makeup designer," told Deadline.
"It would mean that there were scars left there, which she'd need to cover, which would mean she wore a thick white makeup, blocking out that wonderful bottom lip of Margot Robbie's," she added.
Shircore used the same strategy for Robbie's eyebrows, by "placing the blisters and the boils along the areas that I wanted to eventually cover with makeup, thereby changing Margot Robbie's face, and getting her to the iconic look."
The Oscar-winning Guillermo del Toro movie focused on a love story between a mute cleaning lady named Eliza (played by Sally Hawkins) and an Amazonian fish-man (Jones).
"When wearing any kind of a costume and makeup that's this extensive, you become a bit of a nursing home patient," Jones told Wired. "I can't see as well, I can't hear much, I can't feel much, and I got these webbed fingers on — I can't do anything for myself."
For the role, Jones wore a snug, zipped suit that was comprised of foam, latex, and rubber. It covered his body from the neck down and required four people to get him into. His outfit also consisted of a fiberglass helmet that was equipped with "built-in buzzing, whirring mechanics" to move his gills, according to IndieWire.
In an interview with BackstageOL, the actor said that he had amphibian-like hands glued on and the creature's eyes were given the CGI treatment during post-production to look more realistic.
The whole transformation took approximately three hours, which is less time compared to other costumes Jones has worn in other movies, and 40 minutes to remove.
You can watch a time-lapse of the process in this video shared by Fox Searchlight.
Theron gained 30 pounds, had makeup applied to give her skin a blotchy appearance, and wore prosthetic teeth.
"It wasn't about getting fat," the actress told Spliced Wire. "Aileen wasn't fat. Aileen carried scars on her body from her lifestyle, and if I'd gone to make this movie with my body —physically I'm very athletic — I don't know that I would have felt the things Aileen felt with her body."
She added: "It was about getting to a place where I felt closer to how Aileen was living. I didn't want to look at my body and see my natural muscle. That kind of thing would have thrown me off completely in trying to be her."
Hoult told "E! News" that shaving off all his hair to play Nux, who was basically on death's door at the start of the movie, was "freeing."
The various scars on his lips and body were the result of two hours of makeup and to get the chalky skin tone, clay was applied. In order to achieve a thinner physique, Hoult told Screen Slam that he "didn't eat as much and jumped rope a lot."
For her first appearance in the Marvel Cinematic Universe in 2014's "Guardians of the Galaxy," Gillan actually shaved off all her hair. The actress revealed her bald head at San Diego Comic-Con in 2013 and called the move "liberating."'
In 2014, special effects makeup artist David White told Business Insider that Gillan's prosthetic makeup was the "most complex and interesting" to apply. Moreover, it took approximately four hours and 15 minutes to apply and 30 minutes to remove.
By the time Gillan reprised her role as the assassin for the "Guardians" sequel, the process was shortened to two and a half hours and she only had to shave the sides of her head. You can see Gillan transform into Nebula in this video shared by Mashable.
Read more: THEN AND NOW: The 'Avengers' stars before they were famous
Makeup designer Greg Cannom told IndieWire that Bale gained 25 pounds for the role and actually added additional weight for one particular scene. He also wore a fat suit in the film and shaved his head.
Bale's face looked unrecognizable in the Oscar-winning movie because of various types of prosthetics that were applied, from neck and nose pieces to "cheek appliances."
According to USA Today, the whole process took four to eight hours each day.
