Jacob Tremblay is unrecognizable as Auggie Pullman in the new movie "Wonder."
To play the 10-year-old boy with Treacher Collins Syndrome who is the heart and soul of the film, Tremblay, 11, had to endure two hours of makeup each day of filming.
The film, based on R.J. Palacio's 2012 novel, chronicles the struggles of a young boy with the rare disease, known in medical terminology as mandibulofacial dysostosis, that causes abnormalities of the head and face.
"They had a neck piece, a face piece connected to a mechanism to make my eyes droop, contact lenses, dentures and a wig," Tremblay told ABC News. "Wearing the prosthetic helped me to become the character."
Tremblay was cast in the role after producers saw his performance in the 2015 film "Room," in which he played a child born in captivity opposite Brie Larson, who won the Oscar for playing his mother.
Though he hadn't yet read the book "Wonder," he knew about it from his older sister, who had read it.
"I totally wanted to be a part of this because of this message," he said.
That message, "choosing kindness," is also the tagline of the film.
"When I heard that message, I thought I gotta be a part of this film," the young star said.
To prepare for the role, the Canadian-born actor and his parents researched kids with facial differences and found children at The Hospital for Sick Children, also known as SickKids, in Toronto.
"We asked them if they could send me letters," Tremblay said.
He collected all the letters into a binder.
"I would read some letters from the binder before I did some of the serious scenes," he said.
Like Auggie in the film, Tremblay is a huge "Star Wars" fan in real life. In a few scenes in the movie -- spoiler alert -- Chewbaca springs to life from Auggie's imagination. One day, during shooting, the director surprised him.
"They actually got the real guy from 'Star Wars,' said Tremblay, who recognized him the moment he took off his costume.
Since the film's release, Tremblay has continued to spread the film's message of choosing kindness by teaming up with Crest toothpaste as part of World Kindness Day, which was earlier this month.
"Choosing kindness is just as easy as smiling," he said.
Tremblay brought a lot of smiles Tuesday, when he and two other child actors from the film attended a special screening at SickKids in Toronto.
"That was amazing," he said. "The kids who weren’t able to attend the theater, got to watch it in their rooms."