According to Klingon legends, Shadowheart's kingdom was located on Nothra. He challenged the Klingon devil (Fek'lhr) for the right to rule Gre'thor. Though he lost, he earned the devil's respect and was made ruler of all shadows in the mortal world. The story of Shadowheart taught klingon babies to look at shadows only out of the corner of their eyes for when one sees him, it is the person's day to die. In the Nothrani culture, as well as the Klingons, Shadowheart was seen as a symbol of rebellion.
In 2369, the human, Nikolai Rozhenko took the name when he crash-landed on Nothra seeking revenge for the massacre on Lisarion, was taken in by the Nothrani, exposed to the jungle gases and led a rebellion against the Klingon security forces on the planet. (TNG - Shadowheart comics: "The Lion and the Lamb", "Dealers in Darkness", "The Prince of Madness")