Nikolai was raised primarily on the farm world of Gault along with Worf. The brothers were often argumentative, and Worf would later describe Nikolai as "a loose cannon." (TNG episodes: "Heart of Glory", "Homeward")
Nikolai joined Starfleet Academy at the same time as Worf. During his time there, Nikolai got into fights with cadets about his brother, in which Worf had to help him out. Nikolai dropped out after one semester, realizing he was not cut out for the stringent academic setting and did not want his brother's protection. He then decided to return to Gault. (TNG episode: "Homeward"; TNG - Starfleet Academy novel: Worf's First Adventure, TNG - Shadowheart comic: "The Lion and the Lamb")
- Worf's First Adventure, which was published before the name of Worf's human brother was established in canon, gives the character the name "Simon". Nikolai's full name is in accordance with Russian naming conventions; since Nikolai's father is named Sergey, Nikolai carries that name as a patronymic.
The day Rozhenko quit the academy, he cut ties with his parents and returned to Gault. He then traveled to other farming planets before moving to Lisarion and becoming a "great leader." Sergey and Helena considered they lost Nikolai long before his apparent death in a raid on Lisarion in 2369. Nikolai had gone to Nothra to investigate the raid and after a crash-landing and exposure to the Nothan jungle gas, took on the identity of the Klingon legend Shadowheart. Eventually his memory and appearance were restored. (TNG - Shadowheart comics: "The Lion and the Lamb", "The Prince of Madness")
By 2370, Doctor Rozhenko was assigned to a cultural observation post on the planet Boraal II. During this mission, he became overly involved with the native culture, in violation of Prime Directive guidelines, and fathered a child with Dobara, a female Boraalan.
In 2370, the atmosphere of Boraal II was destroyed, but not before Rozhenko was able to transmit a distress call picked up by the USS Enterprise-D. After that ship responded, Rozhenko secretly had his group of Boraalans beamed to the holodeck, which provided the aliens the illusion of still being on their homeworld. Rozhenko then convinced Captain Picard to transplant them to another world, Vacca VI, and Rozhenko remained there with them. (TNG episode: "Homeward")
Shortly after, Doctor Carol Abramowitz, at the request of Starfleet Commander Uxmen, contacted Rozhenko to determine what further actions, if any, were warranted. She found Rozhenko unwilling to budge, and Abramowitz concluded there was little else to be done. (SCE eBook: Fables of the Prime Directive)