Calder is a titular main antagonist of the How to Train Your Dragon graphic novel, Serpent's Heir.
Calder invited Hiccup and his people from Berk in order to investigate the island, Nepenthe, Calder's island, since there are unusual things happening.
Once they reached there, Calder imprisoned the Dragon Riders and he showed them that he is meant to be a dragon and he show them that he is transforming into one by wearing the costume.
Later, it was revealed that the unusulal stuff happened because there are gigantic Foreverwing Dragons hidden. Once Calder held Hiccup's flaming sword, Inferno, Hiccup threw a canister of Zippleback gas on him and it exploded and he falls from the cliff, but survived.
Calder appeared as a tall man with blonde hair. He wears a cloak, but he removed it to reveal his dragonscale tattoo, since he believes he is meant to be a dragon. He later wore a dragon costume.
He is a corrupt official who believes he is meant to be a dragon and the reason is unknown.