From WENN.com

Cruise's casting has been somewhat controversial because he looks nothing like Child's leading man, who is described as being almost a foot taller than the Top Gun star in the books.

But the actor signed on for the role after first checking with the author if he was good to go.

He says, ""Had he said, 'Look, I'd rather you not (play Reacher)', I would not have played the character... (The height) was a characteristic for me. It's not the character.""