The movie "The Blind Side" has become the season's surprise hit, raking in more than $150 million at the box office and earning a Golden Globe nomination -- and Oscar buzz -- for its star, Sandra Bullock.
Director John Lee Hancock told "20/20" he had only read a few chapters of Michael Lewis's book "The Blind Side" when he decided that he wanted to write and direct the movie.
"This was really a terrific story, and it was kind of more of an unconventional mother/son story than it was a sports movie. So about fifty pages in, I was in," he said.
Hancock said he also knew that Sandra Bullock would be the ideal actress to play Oher's adoptive mother Leigh Ann Tuohy.
Watch "The Blind Side: The True Story Behind the Movie" on a special edition of "20/20," Tuesday, Dec. 29, at 10 p.m. ET
"Everybody knows her for her comedy skills and her behavior comedy, and her sharp tongue, and those are formidable skills, but I didn't think that she'd been given the chance to...show off the really great dramatic talent that she has," Hancock said. "I knew that she could pull it off."
Next, the director said he had to find an actor to play her husband, Sean Tuohy.
"I cast Sandy and started thinking about it, I sort of, I realized that there would be a lot of actors that would become wallpaper quickly," Hancock told "20/20." "I needed someone that was comfortable in his own skin, and had the kind of a self-effacing sense of humor."
Country music star Tim McGraw came on board despite initial reluctance to appear in a sports or family movie after his roles in "The Rookie" and "Flicka."
"I read it and just fell in love with the ...characters and the people," McGraw said, "And I gave it to my wife to read, and she loved it as much as I did. It's just rare that you come across a story...that moves you that much."
For Hancock, it turned out that enlisting A-list stars was the easy part. He said the real challenge came when it was time to cast an actor to play Michael Oher -- the "gentle giant" on whom the film centered.
"It's literally a tall order," explained Hancock, "I had seen hundreds and hundreds of tapes and thought, these guys just aren't quite right physically...or they don't have the quality...the movie needed."
At 6 feet 8 inches and 450 pounds, Quinton Aaron was dreaming against all odds of becoming an actor. However, he found very few auditions requiring someone of his stature, other than type roles for bouncers or security guards.
Aaron happened to be working as a security guard in real life when his mom found a casting call online for "The Blind Side." After reading the role description, they instantly felt he would be perfect.
"They was basically looking for a quiet gentle giant. You know, he didn't really say much, he didn't really have a lot of friends, but he was like -- you know, even though he was big, he wasn't -- you know, a beast. He was, like, calm inside and warm-hearted, and that kind of fit well with who I was," Aaron said.
After watching Aaron's audition on tape, Hancock flew him out to Los Angeles for a meeting. It was Aaron's first plane flight and his first time in L.A.