Worf's adoptive father and husband to Helena. Sergey was a chief petty officer aboard the U.S.S. Intrepid, the starship dispatched to aid the Klingons following the Khitomer massacre in 2346.

Sergey Rozhenko and his wife Helena adopted a young Klingon named Worf soon after the massacre. He was one of only a few Klingon survivors of the attack.