Compared to the various other goblins and sentient creatures of the Dark Forest, the Bog King seems to be the most fairy-like anatomically. He wears no clothes, his body covered in armor-like exoskeleton resembling decaying leaves and bark. His limbs are thin, matching the rest of his body, making him the tallest humanoid character in the film. He possesses ears, chin and nose, matching his angular anatomy. He has four matching dragonfly-like wings on his back with various tears and imperfections that do not seem to impede his ability to fly.
The Bog King is known throughout the two kingdoms for being loud, cruel and ruthless, being a frightening figure to both kingdoms. He is shown to be quick to anger, shouting and roaring at the slightest bit of even the meekest of bad news. Ever since the woman he fell for spurned his advances, the Bog King has developed a militant cynicism of love, believing that it was because he was too ugly to be loved. He is visibly repulsed by Dawn's love-sick singing and his mother's attempts to get him a date, and even ends up bonding with Marianne because of it. He made love illegal in the Dark Forest, and took every precaution to ensure that the love potion is never used again, including the imprisonment of the Sugar Plum Fairy, the destruction of every primrose along the border and even kidnapping Dawn as a ransom for Sunny's potion. He is described as having no patience, imprisoning the Sugar Plum Fairy before she could explain why the potion did not work and vocalizing his hatred of riddles.
Despite his imposing reputation, the people of the Dark Forest seem to legitimately care for his leadership and well-being. They have been shown to try and help him find love and became distraught when they thought he died. While he can be abusive to them at times, he does seem to have great restraint for them, ignoring them should they annoy him and even giving his guards a break when they started falling asleep.
He is also shown more than once to have a sweet side, becoming legitimately surprised and sentimental when Dawn makes him a boutonniere and keeping it despite his general disgust with her affections. He is shown to be rather awkward when with a social-equal (like Marianne) or someone who sees him as such (like Dawn) and has a hard time admitting his feelings even when it is glaringly obvious.
He has stated more than once that he "hates princesses", and has ignored nearly every suitor in his way. This could be more out of a distaste towards victims and damsels, as he first bonded with Marianne because she was able to match him in combat.
Powers and Abilities
While possessing no magical powers, the Bog King is shown to possess impressive fighting skills with his staff, being able to defeat nearly everybody in his path. He is also shown to be very strong, being able to lift the skull-entrance of his castle long enough for the others to escape.
His staff is shown to be very durable, being able to block Marianne's strikes with no signs of wearing down. Despite its size, the staff does not seem to be very heavily, both Bog and Marianne being able to lift it easily and is swung around in combat much like a bo. It also seems to be able to make music (the orb on it glowing briefly) should it be strung like a guitar, though whether this is an actual feature to the staff or just a visual narrative quirk by the animators is never clarified.
The Bog King's prisoner, the Sugar Plum Fairy, makes a love potion and gives it to an elf named Sunny who, along with a fairy named Roland, wishes to use it to make Marianne fall in love with Roland and her sister Dawn fall in love with Sunny, but the King recaptures The Sugar Plum Fairy. However, Sunny is able to escape back to the Fairy Kingdom with the potion.
Determined to get the potion back, the King has Dawn taken hostage but during the kidnapping, the potion sprays Dawn in the face and she ends up falling in love with the King, much to his annoyance. Marianne arrives at the King's castle to rescue Dawn and battles the King (Straight On). The battle becomes flirtatious, the King grows to respect Marianne for her sword skill and snarky retorts. His mother notices him smile at her. Griselda decorates a room with tacky romantic tokens and leaves him alone with Marianne. He and Marianne feel awkward about this but bond over destroying the decorations.
The King then tells The Sugar Plum Fairy to make an antidote to stop Dawn being in love with him, but she tells him the only thing powerful than the potion is true love. She narrates this point by revealing the Bog King asked her to use the Love Potion on a girl he was in love with years ago. The creature rejected him regardless, revealing the King's broken heart. Marianne relates to his pain and shares with him their mutual cynicism and distrust of romance.
Despite both saying they trust no one, Marianne suggests they take a flight for fresh air. The King shows Marianne the secret beauty of the Dark Forest; they fall in love while singing the titular song Strange Magic.
They are interrupted when Roland and his army arrive to rescue Dawn and hand over the potion. Thinking Marianne set him up, the King throws her into a spider web and returns home where he finds Roland there with the potion. Roland refuses to hand over the potion unless Marianne and Dawn. The King is prepared to give up the princesses however, even though he has Marianne restrained by his guards, he refuses to allow Marianne to go with her ex-fiance. His refusal ensues a battle between Roland, who is humorously disgusted by Marianne and the King quarreling like an old married couple to which the Bog King asks Marianne “Is that the guy?”. Marianne arrives and helps the King battle Roland who tells his army to tear down the castle. The King holds up a crumbling door so Marianne and Dawn can escape, leading to his assumed death.
Marianne and Dawn mourn the King's death, but he emerges from the ruins off the castle alive and well. Roland still determined to get Marianne to fall in love with him again, gives her the potion. But due to her true love for the King, the potion doesn't work and Marianne knocks Roland into the valley below taking the potion with him. Marianne's sister, Dawn, finds her true love with her longtime friend Sunny; she then encourages her sister and the Bog King to express their feelings (Tell Him). The King and Marianne confess their love for each other and kiss.