It’s a bad idea. Here’s why. One Shot, Lee Child’s title for the 2005 novel, is a great title for a thriller; that, plus Tom Cruise, plus some good ads, should be enough to lure people into the theater. But if you call the movie Jack Reacher, the name of its lead character, you’re telling potential audiences:
1. You should know who Jack Reacher is — you should recognize the name, it should make you excited to see the movie. Which is fine if people are familiar with the Child novels, but you have to figure a substantial portion of the potential audience for the movie has never heard of Reacher or Child. Do you think calling the movie Jack Reacher might just possibly make them feel uninformed, or embarrassed? Here’s this ad for a movie about a guy I’m obviously supposed to know, but I don’t know him, so thanks for making me feel stupid.
2. We’re planning to make more movies about this guy. You haven’t seen this one, but we figure you’ll like it enough to want to see more of them. But potential audiences might think that’s a bit arrogant. Shouldn’t we at least have the opportunity to ask for more movies before you assume we’ll want them?
If I didn’t know who Reacher was, and I saw the commercials and trailers and whatnot, I’d say: who cares? You guys think this Reacher fella is Important and Famous, but I’ve never heard of him. My point being: they should have kept the original title — called the movie One Shot, introduced Reacher to the audience, and then, if the movie did well, made another one with his name in the title.
Remember: the first Indiana Jones movie was called Raiders of the Lost Ark, because nobody knew who Indiana Jones was.