Smolder is a pale-yellow SandWing and the only living brother of Burn, Blister, and Blaze, therefore making him a SandWing prince. He is similar in appearance to Blister, having pale yellow scales, a narrow face, dark lidded eyes and diamond pattern on his scales. He keeps keys, pouches and bells on his neck. Sunny described his voice as sardonic and fairly normal, unlike Blister's voice.
He fought on Burn's side in the Great War, yet Burn seems to dislike him, possibly because he resembles Blister in his appearance. He isn't the only brother of the SandWing sisters, but the other two "made the wrong dragons mad", and were presumably killed.
In The Hidden Kingdom, Blaze says her brother fell in love with a dragon her mother would never agree with, and she broke his heart. This was Smolder, and his girlfriend was Palm, who was never seen again.
In the epilogue of The Dark Secret, he is in Burn's Stronghold speaking to Burn about the dragonets of destiny. He and Burn plot to kill all of the dragonets. He also stated about a prisoner that Burn said was Queen Scarlet. He also stated that he wasn't used to calling Burn "Your Majesty".
In The Brightest Night, Smolder is running Burn's Stronghold while Burn is away, looking "for a certain quintet of dragonets." He leads Sunny to the tower where Burn stores her collection and "special" prisoners, such as Queen Scarlet. He introduces Sunny to his pet scavenger named Flower and proceeds to lead her to her cell in the tower. After seeing how miserable Sunny was, decided that he'd take her out at midday for a walk everyday. He is actually quite a nice dragon, even though it's Sunny thinking.
He later unchains Sunny, and orders Camel to watch her as he organizes troops to defend the stronghold. Thorn and the Outclaws were attacking the stronghold, and Smolder was successfully fending them off. Sunny begs Peril to stop the fight to save her mother, and she does so.
Smolder then leads Thorn, Sunny, and Peril to Burn's collection, on Thorn's orders to see the dead, stuffed NightWing that Burn owns.
Later, Smolder leads Thorn and Sunny into the library and locks them in there, claiming that Burn would kill him if she found out that he let them leave. Thorn and Sunny escape and part ways.
At the choosing of the SandWing queen, Smolder is present and hands Burn Blister's gift. The gift happens to be two dragonbite vipers, one of which kills Burn. Blister and Blaze fight, and Sunny finds the Eye of Onyx and gives it to Thorn.
Smolder apologizes to Thorn, and Thorn claims that it would be hard to forgive him.