Lei Magnus (Japanese: レイ=マグナス Romaji: rei magunasu; alternate trans.: Rei Magnus) was a famous and powerful human sorcerer during the time of the Kōma War. It is common belief among fans that he is one of the Five Great Sages, but official material does not support this claim.

Only a few concrete facts are known of his life. Lei was the inventor of two of the most powerful spells, the Dragon Slave (originally called the Dragon Slayer) and the Blast Bomb. One of the first public displays of the former spell's power was when he killed a 1,600-year-old arc dragon with it. It is unknown if he is the one who created the Demon's Blood Talismans, but they certainly were in his possession for a while.

A fragment of Ruby Eye Shabranigdu resided within the sorcerer, and for the mazoku, one of the objectives of the Kōma War was to awaken that piece. As Hajime Kanzaka explained, the seal on the fragment of Ruby Eye was broken similarly to Luke's: Lei was consumed by hatred towards other humans when he witnessed the bloody massacre of the war fought between human nations in the early years of the Kōma War. Little did he know that the war was staged precisely in order to have this effect by Hellmaster Fibrizo. During the war, Lei Magnus-Shabranigdu gave the Demon's Blood Talismans to Xelloss as a gift in exchange for doing a great favor for him. Whatever this favor was has never been stated officially, but it was hinted to be connected to the mazoku priest's achievements during the conflict.

However, Fibrizo's plan was cut short when Aqualord Ragradia defeated Lei Magnus-Shabranigdu and sealed Chaos Dragon Garv into a human body, at the cost of her life. The fragment (as well as Lei) was frozen in ice and sealed in the Earth. He soon gained the title of "Demon King of the North". Lei and the fragment of Shabranigdu are still alive, but are unable to leave the spot where they are frozen.