He was court sorceror of Burnstein. He used to be Sandra's teacher when she was at the Magic Academy. The land near Klein village used to be his territory but he disappeared from Burnstein. He exchanged Eliotte for a clone, Richard, and was supposed to have Eliotte killed. Gevel ordered him to do this and he obeyed because he feared Gevel would kill him. However instead of killing Eliotte, he had subordinates raise him as foster parents and he intended to expose Gevel's scheme. He wrote the letter that Eliotte's family was supposed to deliver to Rolandia.
Venzern had created the group of Shadow Knights and used to be their first leader. When Richard, Gevel's puppet, became king of Burnstein, Gevel wouldn't have use for Venzern any longer so Venzern fled to Ranzack and had them shelter him in exchange for teaching them magic.
He helped out Carmaine's group to put Eliotte back on the throne of Burnstein because he is one who can confirm Eliotte's identity. He also helped save Louise's life because she is a Growsian which is the only one who can defeat Gevel. Venzern appears at the battle against Richard to help take him down.
Venzern asked Louise for help on a research project and visited Sandra. However he fooled them and used a device to steal Louise's Growshu. He had had a strong interest in what Sandra researched at the Magic Academy as her graduation thesis -- a method to return lost power. He succeeded at researching how to extract Growshu from humans and aimed after Louise who had power of a full solar eclipse Growsian.
After he recovers his full strength he revealed that he is the last king of Growsians and seeks to rule mankind. Venzern is a Growsian back from the era when they ruled a long time ago. He experimented on how to obtain long lifespan and stronger body, so he attempted to fuse his body with Gevel. With such a body he would have the ability to control space-time on a small scale, and his body is able to regenerate immediately when damaged. He also has the ability to teleport so Carmaine's group was at a loss on how to defeat him. They used the Power Stone which made Venzern lose his ability to heal quickly. He threatened to destroy a whole village if they did not give him the Power Stone. Ernest Lyell offered to hand it over to him in exchange for the safety of the villagers. Venzern destroyed it and he threatened everyone with his power full-force. Because he could control time-space, he could prevent the two worlds from separating. If they did, their world would be destroyed, so they would have to depend on Venzern for the sake of their world.
Carmaine's group endeavor to find a way to make another Power Stone and defeat Venzern. With help from the Featherians they managed to find a way, and they finally destroyed Venzern at the time-space control tower.