The evidence:
QED
Apologies if this has been explained already. I admit I haven't seen all the episodes or read any of the books. But this question has been bugging me and I haven't seen a satisfying answer.
In the show, Jack Reacher goes by just Reacher with everyone. No one uses his first name. This isn't strange when it's just his army buddies, but then we meet his family members and they call him Reacher too, even in flashbacks to when he's a little kid. Why would a family choose to address one son by the last name they all share?
The theory: When Jack Reacher's mother, who is French, was pregnant with him, her first choice for a name was Richard. But Richard pronounced the French way sounds awfully like Reacher.
Reacher's dad, seeing confusion ahead, vetoed the name Richard. They settled on Jack instead.
But Mom got her way in the end. She starts calling her new baby Richard--first when it was just the two of them, then all the time. She was his mother, who was going to stop her? Eventually the name caught on with the rest of the family. They even adopted her confusing French pronunciation. Dad was the last to give in.
And events played out exactly as he'd feared. As little Jack grows older and goes to school, his nickname leads to awkward conversations. The family gets tired of explaining "no, not Reacher, we said REE-shar. It's French."
Eventually, they throw up their hands and say "Fine, yes, we call him Reacher. Just Reacher. And we're not taking any more questions at this time."
Bonus theory: why was Reacher's mom so fixated on the name Richard? Because when she first met Reacher's dad, she thought *his* name was Richard. For the first few weeks of their courtship, she was enamored by her new beau Richard, until one day he clarifies that his name is actually Stan (wtf).