The Osprey has had a rocky road to usage by the military. It emerged as a result of the failed Desert One Operation in Iran. The military decided that it needed a transport that could take off like a helicopter and fly like a plane. This would let it speed to its target and land just about anywhere.
Bell Helicopter had been working on the tiltrotor concept since the 50's and was able to successfully use a prototype in the 60's. The military didn't see a need for this design at the time, so it was shelved.
The Osprey had a troubled development as a few of the prototypes crashed. At one point, it looked like the whole program would crash. They were able to work the bugs out.