Atram Galiasta

An oil magnate. In the Fifth Holy Grail War, he was Caster’s Master.
The original Fate/stay night and Case Files were set to take place in the same world, but upon seeing his first appearance in the UBW anime, the author was brought to tears of laughter. Though in his first appearance he was described as a middle-aged man of medium build, when it was said he would “change a little” for that adaptation, that “little change” ended up being enormous!
The basic concept was a Shinji with a decent amount of skill and success (See Fate/stay night). With El-Melloi II’s concept as a “Shinji’s Revenge” story, the two had an odd sympathy for each other, though perhaps that was the natural result. As the UBW anime demonstrated, he was fundamentally a bad person, but being a bad person doesn’t mean he had no redeeming or lovable qualities whatsoever.
After Volume 3, up until the point he departed for the Fifth Holy Grail War, he visited El-Melloi II about once a week to brag, ensnaring himself in a diplomatic battle between himself, Melvin, and Yvette. In a way, you could call them the three monsters hanging around El-Melloi II. There was even an incident shortly before he left for the Fifth Holy Grail War in which the three of them, once and only once, worked together.
By the way, while in the middle of Volume 2 he was wary of the Lord of the Faculty of Creation Inorai, he had no such fears of Touko. “Someone from the Far East being a Grand must be some sort of mistake,” was his thought process.

Lord El-Melloi II Case Files material: Lord El-Melloi II Case Files Glossary