The Klingon warrior who fathered Worf and Kurn, died in the Romulan attack on Khitomer in 2346 and was posthumously and falsely branded the traitor who betrayed the outpost.
Mogh was the head of a respected Klingon house and the father of Worf and Kurn. Suspecting that his rival Ja'rod was plotting with the Romulans, he followed him to the Khitomer outpost, taking his wife and elder son and leaving the infant Kurn with his friend Lorgh. Mogh and his wife died in the massacre of 2346; Worf was pulled from the ruins by Sergey Rozhenko.
In Sins of the Father the High Council accuses Mogh of sending Khitomer's defence codes to the Romulans. Worf and Picard establish that the traitor was Ja'rod, father of the powerful Duras, but Worf accepts discommendation to prevent civil war. The family name is restored in Redemption.
Mogh is never seen. His house is stripped of its lands by Gowron in The Way of the Warrior, and Worf later joins the House of Martok.