He is voiced by Takahiro Sakurai in Japanese version,Matthew Gravelle in English version.
Jasper is the childhood friend of Hendrik, they're trained as junior knight by King Carnelian in the Helidor Castle.
World of Light
Jasper made a pact with Mordegon. By assisting him, he will be promised with migjt and power since he is jealous of Hendrik, who ignored him and accept his knighthood during a ceremony held by the king. Than after the Luminary is locked up by Mordegon, who possessed King Carnelian. Mordegon ordered Jasper to kill everyone in Cobblestone, which is the village where the Luminary came from, but is stopped by Hendrik.
Later, Jasper arrived Gondoila and is seen talking to monsters by Mayor's son. Jasper than silenced him by using magic. After the boy is cured. Jasper and his !en captured Erik, who is one of the member of the Luminary's party. He than intended to use Erik to lure the Luminary out, but seems to be defeated easily. However, he than summons a giant squid monster called Tentcular to attack the Luminary, who is on a ship. However than giant squid is scared away by Gondoila merchant ships. Jasper than tell the Luminary that his luck will run out one day.
He later went to the Royal Library and released Krystalinda the ice witch and told her to kill Hendrik, but the witch redeemed herself instead.
Later, at the Yggdrasil, Jasper attacked the Luminary by surprise and successfully knock him out while he is ready to claims the Sword of Light. Mordegon than take the Sword of Light and turns it into the Sword of Shadow who than destroyed the Yggdrasil. Mordegon than gave Jasper the silver orb and let him became the supreme commander of Spectral Sentails.
World of Darkness
After the fall of the World Tree, Jasper has taken up residence in the now riuned Helidor Castle. He is than found sitting on the throne when found by the Luminary and Hendrik.
Jasper than taunt Hendrik about how easily he was tricked and how he join force with the Luminary. He than have a fight with Hendrik and reveals the reason of his actions
After Hendrik beat him back, Jasper retreats and transform himself into his demon form and order Tyriant the Spectral Sentail to finish them, however Tyriant was destroyed by the Luminary and Hendrik.
Jasper is than not seen again until the Luminary reached the Fortress of Fear. He than watch Indignus, the penultimate Spectral Sentail fight the Luminary's party, who was also defeated.
Jasper than created an illusion of Veronica, the deceased member of Luminary's party to ambush them, however the illusion was destroyed by Serena with her lyre.
Hendrik than correctly assume that Jasper was behinded this dirty act. Jasper than confirms this and transform into his demon form -Jasper Unbound to fight the party, but he is defeated too.
Jasper than made an last attempt to defeat the Luminary by forcing him to fight Mordegon one-on-one, but this plan is also foiled as the party is able to overcome his attack. Jasper than began to fade away and he comfessed that he is just envious of Hendrik, who than reply by telling Jasper that he thought Jasper is always stronger before Jasper died.
World of Lost Time
After the Luminary returns to the time before the destruction of the Yggdrasil, Jasper attempted to ambush him again at the Yggdrasil, but this time the Luminary is able to deflect his attack with the Sword of Shadow, frustrated, Jasper than attacks them, but is defeated this time. Jasper than made a desperate attack, which the Luminary blocked, but destroying the Sword of Shadow in the process, King Carnelian and Hendrik than enter the Yggdrasil again. Carnelian than killed Jasper before he can reveal that Mordegon is possessing him.
Jasper is a man with cruel features and a youthful appearance. He has fair skin, small yellow eyes, and chin-length light blond hair with some of the fringe covering the right side of his face and a long ponytail that goes down to his waist. He wears an armour of silver and gold knight's armor over chainmail, white trousers, and a white pair of boots. Attached to his armor is a long white cape with red lining that reaches down to his feet. Emblazoned on the front of his armor's breastplate is a golden two-headed eagle, which is the symbol of Heliodor. When his master conquers all of Erdrea, he wears a black outfit that resemble the one of Dhoulmagus's, his skin is darker, eyes become yellowish, his ponytail is tucked into the outfit, and his fingernails are black. When transforming into his Unbound form, he becomes a muscular demon. His hair is completely loose. And fur appears on his arms and legs.
Jasper is a skilled tactician that is able to defeat an army of monster with just a few soldiers. He is also good at marine battle. Since he is trained to be a kinght in his childhood with Hendrik, he has good swordmanship. Since he has done a pact with Mordegon, he is able to use dark magic. Jasper is shown to be envious towards Hendrik for being more well-liked. When he becomes the supreme commander of spectral sentinels, he becomes very arrogant and cold-blooded.
- Jasper can be said to represent envy, as he was jealous of Hendrik.