Caster of Red is the Caster-class Servant of Jean Rum of the Red Faction in the Great Holy Grail War of Fate/Apocrypha.

Placing the importance of the Story above all else, he lies and cheats and by any means conduct himself that he might witness the unfolding of a grand tale, beautiful beyond compare. Consequently, he tends to distance himself from mentality of the "participant," taking instead the perspective of an abstract, "Authorial" third person. His regard for others differs by individual, dependent on their qualification as a special existence, or "protagonist." He interacts with "normal humans" only in a shallow, dismissive manner, and expresses an extreme interest in "protagonists." In slight narcissism, he frequently drops such self-authored quotes as, "Things bad begun make strong themselves by ill." He's taken a liking to certain terminology from modern fiction, such as "Death-Flagging." With short and effective words, he brings to light that what humans usually keep hidden. This is like suddenly being poked by rambling, incongruous words, so one would probably feel shocked.

As the world is the greatest story ever told to him, or so it ought to be in his eyes, he willingly employs deception, provocation, or anything else for the sake of spinning the story. He greatly loves those who are out of the ordinary from the bottom of his heart, perusing the tales they spin. With greatly exaggerated outbursts of emotion, he acts as he wishes, gracefully admitting that it is suitable to call him a trickster.

(Source: Type Moon Wikia)