This month, Marvel dropped the first teaser trailer for the "Doctor Strange" movie. But, after seeing the characters in the upcoming film, some viewers accused Marvel of whitewashing.

Specifically, the critics did not appreciate that Tilda Swinton was asked to play the Ancient One, a mystic character who became the mentor of Doctor Strange. In the Marvel comic book universe, the Ancient One was born in Tibet, which indicates that the character is Tibetan.

For critics, Marvel and producers of the film should have closely followed their original material by casting an actor or actress that has a similar ethnic background. The company, however, defended its decision in going with Swinton and maintained that it promotes diversity in its projects.

"Marvel has a very strong record of diversity in its casting of films and regularly departs from stereotypes and source material to bring its [Marvel Cinematic Universe] to life," the company said in a statement to Mashable.

"The Ancient One is a title that is not exclusively held by any one character, but rather a moniker passed down through time, and in this particular embodiment is Celtic," Marvel continued. "We are very proud to have the enormously talented Tilda Swinton to portray this unique and complex character alongside our richly diverse cast."

On the other hand, Robert Cargill, the screenwriter of "Doctor Strange," was not so calm when explaining the decision regarding the portrayal of the character. According to him, his conceptualization of the character was influenced by the current political environment, particularly by the conflict between China and Tibet.

"The Ancient One was a racist stereotype who comes from a region of the world that is in a very weird political place," he told Screenrant. "He originates from Tibet, so if you acknowledge that Tibet is a place and that he's Tibetan, you risk alienating one billion people who think that that's bulls***and risk the Chinese government going, 'Hey, you know one of the biggest film-watching countries in the world? We're not going to show you movie because you decided to get political.'"

As for the film, "Doctor Strange" is scheduled to premiere on Nov. 4, 2016. Aside from Swinton, the film also stars Benedict Cumberbatch as the titular character, Chiwetel Ejiofor, Rachel McAdams and Michael Stuhlbarg.