Don John the Flame Lord is a Flame Person who first appears in the episode "Wizard Battle" as a contestant in the Wizard Battle. When Abracadaniel is explaining that opposite wizards would fight each other, Flame Lord is seen squaring off against Ice King. However, Ice King cheats by knocking him out with nunchucks. He is also mentioned in the backup comic in Issue 2 called "After the Show." He later makes a cameo in "Wizards Only, Fools" as the Wizard Police chase after Finn, Jake, and Princess Bubblegum through Wizard City.
In "The Red Throne," he helps Flame King overthrow Flame Princess in return for her hand in marriage. When Flame Princess refuses, however, Flame Lord feels cheated and has a fistfight with Flame King. During this fight, Cinnamon Bun frees Finn and Flame Princess from their prison and has Flame King returned to his lantern together with the Flame Lord.
Flame Lord is a wizard who wears a huge red coat that covers his body. He has long, red- and purple-striped horns on his head. He wears a mask that has a dark-purple face and yellow eyes with red slit pupils on them. He also has yellow lips and a red slit mouth. He has fire on his shoulders and hands and has a black belt with a flaming buckle and two large, muscular dark-purple legs.
In the episode "The Red Throne," he loses his sleeves and appears more muscular since his last appearance.
In the episode "The Red Throne," Flame Lord helped Flame King with overthrowing Flame Princess and taking over the Fire Kingdom. However, he felt as if he'd been cheated after that, and he got into a fist fight with Flame King. In the end, Flame Princess trapped both of them inside the lantern together and took her throne back again.
Flame Lord seems to have affection towards the robust princess, helping the Flame King to reclaim his throne and locked her up in order take her hand for marriage. However, when Flame Princess, who does not have any feelings for him, rebukes him and says that she'll never marry him, Flame Lord feels cheated and fought him. When the Fire Kingdom citizens seize the King, Flame Princess runs to him and punches him with full force and locks him up with Flame King.
- His title, Flame Lord, may be a reference to the Fire Lord in Avatar: The Last Airbender.
- The name Don John is likely a reference to the name of the villain of the William Shakespeare play Much Ado About Nothing.