Kurn is Worf's younger brother, a Klingon officer who served aboard the Enterprise-D and later had his memories erased to escape his family's ruin.
Kurn is a son of Mogh and the younger brother of Worf. When Mogh took the young Worf to the Khitomer colony, the infant Kurn stayed behind on the Klingon homeworld and was raised by the family friend Lorgh, growing up unaware of his true parentage.
As a commander, Kurn came aboard the Enterprise-D through an officer exchange program and revealed himself to Worf just as the High Council moved to blame Mogh for the Khitomer massacre. Worf accepted discommendation to shield his brother and the Empire. Kurn later commanded his own bird-of-prey, backed Gowron during the Klingon Civil War and won a seat on the council. When Worf opposed the Klingon invasion of Cardassia, the House of Mogh was stripped of its lands and honor, and a despairing Kurn sought death. Worf instead arranged for his memories to be wiped, and Kurn began a new life as Rodek.
Kurn's story shows the heavy price that Klingon politics and family honor exact, and it adds depth to Worf's divided loyalties between Starfleet and the Empire.