In 2151 the Klingon courier Klaang crash-landed in Broken Bow, Oklahoma, and Enterprise's mission to return him became humanity's first formal contact with the Klingon Empire.
Klaang's ship came down in a cornfield while he was fleeing Suliban pursuers, and the farmer who found him shot him. The Vulcans advised leaving him to his own people, but Starfleet decided to take him home aboard the newly launched Enterprise. The Suliban later abducted him, and Archer's crew tracked him down and rescued him.
Klaang was carrying evidence that the Suliban Cabal was trying to provoke a civil war within the Klingon Empire. Once Enterprise delivered him to the Klingon High Council the plot was exposed, though the encounter left the Klingons wary of humans for years.