The butler of the Phantomhive household, Sebastian Michaelis is akuma de shitsuji desukara, literally "a demon and a butler" or "one hell of a butler". He is actually the demon with whom Ciel Phantomhive has formed a contract with, to serve him and protect him until he fulfills his goals.
And of course, as soon as that happens, Sebastian will take Ciel's soul; as their contract states.
A rather splendid cosplay of the demon "servant". It would be interesting to know why exactly he would go to such lengths to get Ciel's soul. I wouldn't think demons would work so hard for just any soul. Great cosplaying!