Although granted a lion's head due to the summoning, Caster's intellect is undiminished, allowing those familiar with him to realize "ah, this is indeed Edison" after a bit of conversation. He has a very straightforward personality, and it is said there are not many points of caution for the Master when dealing with him as a Servant. He does unconsciously repeat the work habits he had in life, so careful attention is recommended to the Master so as to keep him from sleep deprivation or overwork. Due to his rivalry in life with Tesla, they will have all relations inevitably break down into a fistfight upon both manifesting as Servants.