"I wish I had a picture of my face," Momoa recalled at a recent press conference in New York.
"I'm the last person who should be hired for Aquaman. I thought I'd be playing a villain."
The 39-year-old actor, who is of Hawaiian, German, Irish and Native American descent, went on to say he initially thought someone like his blonde, Caucasian co-star Patrick Wilson would get the job since he more closely resembles how Aquaman appears in the comic books.
Snyder had the radical idea to cast against type, however.
"To be the first mixed-race superhero at 2018 -- you're like, 'Really, is there not one?' -- that is a huge honor."
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Executive produced by Snyder and directed by James Wan, "Aquaman" is an action-packed, visually stunning and frequently funny origin tale that explains how Arthur was born in New England as the son of Atlanna, queen of Atlantis, and Thomas Curry, a human lighthouse keeper.
When Arthur is a toddler, soldiers from Atlantis track down Atlanna (played by Nicole Kidman) and force her to return to Atlantis and marry the fiance she left behind.
She has a son Orm with the king who decades later (played as an adult by Wilson) plans to wage war against the surface world because he feels its inhabitants are polluting the waters and destroying Atlantis.
Amber Heard's Mera tries to persuade Arthur -- who is blessed with extraordinary strength and the ability to communicate with sea creatures -- to take his rightful place as the ruler of the underwater world, even though it pits him against Orm, her fiance.
Arthur initially turns her down, but decides to help after she saves his father (played by Temuera Morrison) from drowning.
Momoa, who was born in Hawaii and grew up in Iowa, said he connected to Aquaman, a man he describes as a "reluctant hero" torn between two worlds.
"I didn't need to go through what Drogo did to become him," the actor said of the violent king he played on "Game of Thrones."
"But it is neat to relate as someone who is truly from two different cultures," he said, pointing to Aquaman.
"Hawaii definitely doesn't know anything about Iowa and Iowans don't know anything about Hawaii, so that was something that I could draw upon."
Another similarity between Momoa and Aquaman is they were both raised by a single parent.
"I just had me and my mother my whole life," said Momoa.
The actor said he was looking forward to watching "Aquaman" with his family because it is the first thing he has starred in that is appropriate for his two young kids with actress Lisa Bonet to see.
"I'm going to be really probably emotional and affected. And being able to hold their hands, it's going to be a really cool moment," he said.
Wan said he hopes "Aquaman" shows that the actor known for his dramatic work in "Braven" and "Frontier" is also comfortable and capable as a comic or romantic lead.
"I just want to speak English. I don't want to fight anymore," Momoa quipped.
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