Klaang was a Klingon courier in the service of the Klingon High Council during the 22nd century.
In 2151, Klaang met with a Suliban female named Sarin on Rigel X, where Sarin provided him with proof that the Suliban Cabal had been attempting to destabilize the Klingon Empire by staging attacks, making it appear as if one house was attacking another. To do this, she covertly injected the information directly into Klaang's DNA, so that it could be safely transported back to the High Council.
Upon leaving Rigel, Klaang was pursued by two Suliban soldiers attempting to retrieve the evidence, forcing Klaang to crash-land his vessel on Earth, in the town of Broken Bow, Oklahoma. Klaang was eventually successful in killing the soldiers by luring them into a grain silo and destroying it with his disruptor, but sustained serious injuries himself when he was shot with a plasma rifle by a farmer named Moore, on whose land Klaang had crashed.
Klaang was subsequently transported to Starfleet Medical in San Francisco, where he was put on life support and treated by Doctor Phlox. Soval, the Vulcan ambassador to Earth, recommended disconnecting Klaang from life support and allowing the Vulcans to transport his body back to the Klingon homeworld, Qo'noS, but was overridden by Starfleet admiral Forrest, who agreed to let the crew of the Enterprise NX-01 return him alive. En route to Qo'noS, however, Enterprise was boarded by a group of Suliban soldiers, who abducted Klaang and transported him to a helix, where he was interrogated by Cabal leader Silik. Klaang was later rescued by Captain Archer and returned safely to the Klingon High Council Chamber, where the proof given to him by Sarin was extracted from his blood, averting a Klingon civil war. (ENT: "Broken Bow")
Less than one month later, Subcommander T'Pol mentioned Klaang twice while trying to explain to Vorok – the commanding officer of a Klingon battle cruiser who was threatening to destroy a Xyrillian starship – that the Klingons were in Archer's debt since he had returned Klaang to the Klingon Empire. (ENT: "Unexpected")
Later in 2151, Captain Archer privately expressed regrets to Commander Tucker about having launched before Enterprise's systems were on-line. However, Tucker reminded Archer that, if the starship's launch had been delayed any longer, Klaang's body would have been sent back to the Klingon homeworld "in a box," a fact that Archer claimed he kept reminding himself of. (ENT: "Silent Enemy")
While imprisoned by Tandarans at Detention Complex 26, Captain Archer was questioned by Colonel Grat – who ran the detention complex – about the Suliban, Grat making two indirect references to Klaang as a Klingon. The colonel told Archer that Klaang had been chased by two Suliban soldiers and reminded the Starfleet captain, in response to Archer feigning ignorance over Klaang's Suliban pursuers, that Enterprise had returned Klaang to his homeworld. (ENT: "Detained")