Valper Galilei was a member of the organization called Grigori and one of the main antagonists in Volume 3 of the light novels.
Valper had the appearance of a bespectacled elderly man with gray hair and moustache, wearing priest clothes.
Valper had a huge love for Holy Swords and was fascinated by the legend of Excalibur since childhood. Upon finding out that he could not use Excalibur, he fell into despair and held admiration for those that could wield Excalibur. That feeling became so powerful that he started to conduct an experiment to create those who could use them. When his experiment proved unsuccessful, he decided to dispose of the children that were used in the experiments, which resulted in his banishment.
Valper Galilei was the person in charge of the "Holy Sword Project" and performed human experiments to find people who were able to use the seven pieces of Excalibur, and disposed those who were not capable of doing so. Due to this, he was excommunicated from the Church. Seeking revenge from the Church, he allied himself with the Fallen Angels.
Years Later he appears as one of Kokabiel's accomplices and intended to start a war against the Church as part of his revenge. It was during that time that he reveals that the Holy Sword Project was, in fact, successful. However, there was a requirement to wield Holy Swords, in which the wielder needed a mass property of light attribute in their body. This is the reason why Valper removed the light property from the test subjects and transferred it to someone that had a capacity to wield a Holy Sword. He was later killed by Kokabiel who stabbed him with a spear of light after he realized that in the Great War between the Three Factions, the Four Great Satans were not the only ones that died but God as well.