Tom Cruise? Really?

That’s the question that Lee Child, author of the popular Jack Reacher thriller novel series, has been fielding for the past year about the casting of Cruise in the lead role of “Jack Reacher,” a film adaptation of Child’s “One Shot” (2005), in which Reacher — an ex-military police officer who wanders the country righting wrongs — investigates five apparently random killings by a sniper. Directed and adapted for the screen by Christopher McQuarrie (“The Usual Suspects,” “The Way of the Gun,” “Valkyrie”), the film will be released by Paramount on Dec. 21.

As Child explained wryly during a recent book tour stop in Chicago, the search for an actor to play Reacher took place over a number of years. Hundreds of names were “bandied about,” as he put it: Liam Neeson? Daniel Craig? Hugh Jackman? Gerard Butler? Russell Crowe? Josh Brolin? Jason Statham? How about a black Reacher, maybe Will Smith or Denzel Washington?

But the search repeatedly stalled over finding someone with Reacher’s imposing size: 6-feet-5-inches tall, 250 pounds. “It was completely impossible to find a physical facsimile of Jack Reacher in Hollywood,” Child said. “There are none—not even remotely close. The people you think are 6-feet-five and 250 pounds are not. Most of them are at least seven or eight inches shorter than the fictional Reacher. It got to the point where people were saying, ‘What about this guy who’s nine inches shorter than Reacher? He’s better than this other guy who’s nine and a half inches shorter than Reacher.’ ”

Although Child did not have casting approval, he was part of the discussions, and it was he who spun the search in new direction. “Absolutely Reacher is a big guy, no question about it, but he’s also intelligent, intimidating, he gives off a certain vibe,” he told the creative team. “What if we got everything except the size? How would that work?”

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That new thinking led them to Cruise, but his casting set off howls of dismay across the Internet among Reacher fans, primarily because of the vast physical difference between the actor (an extremely fit but not exactly beefy 5-feet-7) and the character as described in the books. “I’ve got a picture in my head of Reacher,” went a typical comment on Deadline.com, “and don’t want it replaced by this twerp.” Other commenters pointed out that Cruise is an Oscar-nominated actor who can play intense, intimidating characters (as he did in “Collateral”) and has been embraced by audiences worldwide as the star of another blockbuster action series, “Mission: Impossible.”

Child, who has seen the film, insisted that the casting gamble has paid off. “It works very well, because Cruise is an odd mixture of two things,” he said. “On the outside, he’s a movie star and a celebrity. But on the inside, he’s a a character actor who wants to get into a role through the script, through the words, and wants to inhabit that world. If you don’t know Reacher [from the books], it’s just a brilliant movie. If you do know Reacher, for the first two or three minutes you’re going to think, ‘This is weird.’ But after the first two or three minutes, you buy into it, it sucks you in, and he convinces you. And at the end of the movie you think, ‘What was I worried about?’ ”

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