Being noted as an ancient Dragon that resided with others of his kind at Darksmoke, it was known that Granamyr lived during the terrible time when his people and those of Humans fought one another in Eternia's distant past. This was until a truce was settled between the two where the Dragons decided to leave the rest of the world and live in isolation at Darksmoke. Granamyr himself is over 10,000 years old as it was stated he hadn't had a good laugh since that time. At some point during the past, it was known that the evil dragon Shadow Wing was an opponent of his who was later imprisoned in an obelisk to shield the world from his evil. Granamyr's great power made him a powerful sorceror and was empowered by the mystical fires from the Pit of Shadows.
The She-Ra:Princess of Power episode Darksmoke and Fire features Adora accidentally being thrown in to Eternia's past, where she witnesses the battle between the dragons and humans firsthand. It is revealed that the war was started by a wizard seeking to set the humans and dragons against each other. To that end he carried out an attack on a human food supply, and then blamed it on the dragons, provoking them in to declaring war against the dragons.
As lord of the dragons of Darksmoke, Granamyr is one of the oldest, wisest, and most powerful beings on Eternia. He evens states that Skytree is the only being older than himself. He is depicted as a huge European style dragon with red scales, wings, and a dark gray helmet. He speaks softly with a refined accent which betrays a learned and patient nature.
He is one of the few dragons of Darksmoke seen in the series, as the dragons generally shun contact with outsides in general and humans in particular. He and the rest of his species have a generally low opinion of humanity, although He-Man and his heroic deeds have slowly changed his views, convincing him that "there may be hope for humans yet."
According to an interview with Larry DiTillio that was included with the season 1 part 2 DVD set of He-Man and the Masters of the Universe, Granamyr was created because Ditillio wanted to pit He-Man against a foe that he could not defeat physically. Further, in the course of the conflict it would be apparent to both He-Man and Granamyr that He-Man could not win by force alone, and that he would have to find some other solution.
In the same interview Ditillio says that he considers The Dragon's Gift to be the best episode he has written.
He also mentions that the name Granamyr was from a role-playing supplement.
He-Man and the Masters of the Universe (classic cartoon)
She-Ra: Princess of Power