The Deathjester is the reason why Kevin and Carlie's adventure began in Seiken Densetsu 3, however, Kevin and Carlie's adventure began because of this person for two separate reasons. For Kevin, it was turning Karl the Wolf against him by dark magic, thus resulting in Karl's death. But, the Deathjester tells Kevin that reviving Karl is indeed possible, thus telling him to go to Wendel to see the Priest of Light. This is what begins Kevin's adventure. For Carlie, after escaping from Wendel, she begins to go find Heath. Heath takes the Black Curse spell that the Deathjester tried to cast at Carlie, when Heath is rendered unconscious, the Deathjester steps in and kidnaps him, easily shoving Carlie aside. The Deathjester knows dark magic and is the servant of the Masked Mage, the final boss of Kevin and Carlie's storyline.
In combat, the Deathjester is a very fearsome foe in the art of magic, particularly with the elements of Earth, Air, Water, and Fire.
A character called Goremand appears in Sword of Mana. His physical appearance and behavior (including eating souls) is very similar to Deathjester. His name supports the connection as well as Deathjester is called Deatheater originally, and Goremand is a pun on "gore" and "gourmand". Because Sword of Mana is heavy on cameos it's uncertain if they are supposed to be the same character though.