He turns out to be the true Servant Solomon, who uses the wish gained by winning the Holy Grail War to incarnate himself as a human in order to experience all that he hadn't in life. He uses his final Noble Phantasm, Ars Nova, to erase himself from existence and give the heroes a fighting chance at defeating Goetia at the final battle in the Solomon singularity.
Not to be confused with Chaldea no Mono, who has orange eyes instead.
