Born in 2345, the son of Mogh and younger brother to Worf.
When Kurn was only one year old, his family moved to the Khitomer outpost, and young Kurn was left in the care of family friend Lorgh.
Both of Kurn's parents were killed in the Khitomer massacre of 2346, and Kurn was raised by Lorgh.
Kurn was not made aware of his true parentage until he reached the Age of Ascension.
As an adult, Kurn joined the Klingon Defense Force.
In 2366, Kurn became aware that High Council member Duras had falsified evidence to make it appear that Mogh had betrayed his people at Khitomer. Kurn joined with his brother, Worf, to challenge this injustice, but found the High Council little interested in uncovering the truth. Instead, Worf was forced to accept a humiliating discommendation to avoid a political expose that would have resulted in his brother's death and may have plunged the empire into civil war. (Sins of the Father [TNG])
Kurn opposed Gowron's bid for the council leadership following the death of K'mpec in 2367. Kurn nevertheless obeyed Worf's decree that Gowron was the rightful leader, and lent the support of his ship, the Hegh'ta, and three other Klingon squadrons to Gowron. Kurn's assistance was critical in preventing an overthrow of the Gowron regime by the Duras family during the Klingon civil war of 2368.
In return, Gowron restored rightful honor to the Mogh family name. (Redemption, Parts I and II [TNG])
Following the victory of Gowron's forces over Duras' during the Klingon civil war, Kurn was rewarded for his service to the empire. He was granted a seat on the High Council. (Rightful Heir [TNG])
NOTES: Worf also had a human stepbrother, named Nikolai, the son of Sergey and Helena Rozhenko, mentioned briefly in "Heart of Glory" [TNG] and later seen in "Homeward" [TNG].