"Who is Jack Reacher?" That question gets asked a lot in this flaccid thriller adapted by Christopher McQuarrie from Lee Child's series of novels. Basically he's Tom Cruise being a tough guy, someone every dame from the old lady at the bus ticket counter to Helen (Rosamund Pike), the assistant DA, moons over. He's a vet with a particular set of skills who seeks the kind of justice the law can't provide. He dislocates arms, crushes skulls, and smashes '70s muscle cars in high-speed chases. He never gets beat and he's never wrong, and he's a bore. Here he's summoned mysteriously by a suspect in a Pittsburgh mass slaying, and, despite dumb questions from Helen, follows an obvious trail of clues that leads him to the evil, sclerotic eye of Zec (a disappointing Werner Herzog). Is it all a joke? If Herzog directed, he could have cranked up the absurdity to a Bad Lieutenant level. As it is, the answer to the question "Who is Jack Reacher?" is — who cares?