Sergey Rozhenko was a retired Starfleet chief petty officer and warp field specialist formerly assigned to the Excelsior-class USS Intrepid under Captain Drew Deighan. Rozhenko was married to Helena Rozhenko and had one son, Nikolai Rozhenko. (TNG: "Heart of Glory", "Family", "Homeward") Both he and his wife were of Belarussian ancestry.
Sergey was serving aboard the Intrepid in 2346 when the ship answered a Klingon distress call following the Romulan attack on the Khitomer outpost. In the wreckage of the outpost, Sergey discovered a young Klingon named Worf. Through an act of kindness, Sergey and Helena fostered Worf. (TNG: "Heart of Glory", "Sins of the Father")
After some time, they returned to Earth. Sergey occasionally took his sons camping in the Ural Mountains. (DS9: "Change of Heart") Worf eventually left his family to attend Starfleet Academy. The Rozhenkos continued to live out their retirement in the same dwelling for a number of years to follow. (TNG: "New Ground")
In 2367, the Rozhenkos visited the USS Enterprise-D while it was docked at Earth Station McKinley following its encounter with the Borg. They transported aboard from Earth Station Bobruisk. During their visit, they received a full tour of the Enterprise-D (excluding some areas due to repairs), and later both parents shared their concern and showed their support for Worf's recent discommendation following a conversation with Guinan. (TNG: "Family")
Later that year, Sergey and Helena met the Enterprise-D at Starbase 73 to take their grandson, Alexander, back to Earth. They intended to provide him with a home and a family following the death of his mother, K'Ehleyr, something Worf would not provide on his own. (TNG: "Reunion")
By 2374, Alexander had decided to join the Klingon Defense Force. Sergey and Helena were not happy about the decision, but when they realized Alexander was determined to enlist, they supported him as they always had. (DS9: "Sons and Daughters")