A Romulan attack on a Klingon colony.
In 2346 the Klingon outpost on Khitomer, near the Romulan border, was destroyed in a surprise Romulan attack that killed about four thousand Klingons. A Starfleet ship, the USS Intrepid, answered the distress call, and Chief Petty Officer Sergey Rozhenko found a young boy, Worf, in the ruins. Rozhenko and his wife Helena adopted Worf and raised him on Earth.
Worf's father, Mogh, was later accused of having given the Romulans the codes to the outpost's defences. In the Next Generation episode Sins of the Father, Worf learns that the real traitor was Ja'rod, father of Duras, and that the High Council had chosen to blame Mogh because Duras's family was too powerful. Worf accepts discommendation to protect the Empire and to shield his brother Kurn.
Worf's family honour is restored in Redemption, when he and Kurn back Gowron in the civil war against the Duras family. In Birthright, Worf discovers that some Klingons captured at Khitomer had been living in a secret Romulan prison camp.