"I am one hell of a butler."
Sebastian is a dutiful and dedicated butler to Ciel. He follows each order faithfully, while always ensuring that the Phantomhive house runs smoothly. As such, he is noticeably annoyed whenever they end up behind schedule.
Despite this, he does not appear to truly care about Ciel or his well-being, as he frequently teases Ciel and occasionally puts his life in danger for his own amusement. He calls Ciel a "brat" who treats his workers rudely. However, despite all the troubles he goes through on a daily basis, he has said that he doesn't think it's such a bad way of life.
He finds humans, in general, to be difficult creatures, but he also thinks that their struggles and lofty goals make them interesting. He has also stated that he would never speak falsely or lie, unlike humans.
Sebastian seems to find the fear of others (especially towards him) amusing and uses their fear to manipulate them into doing what he asks.
Despite his ability to appear like a perfectly normal human, especially one who is able to smile, be cheerful, and be understanding, Sebastian is, in actuality, quite heartless and malicious.
He adores cats of all types, because they do not do or talk about useless things and there is nothing cuter.Parallel to his love for cats, he despises dogs, because they make loud, barbaric sounds. He also keeps several cats in his wardrobe. Sebastian never passes by a cat on the street without stopping to admire it.
Additionally, Sebastian does not sleep, except as a luxury, and frequently does tasks for Ciel at night. He also views money as rubbish and is more than willing to give out generous amounts of pocket money given to him.
Little has been revealed about Sebastian's history, except that he first came to Ciel after Ciel was about to be sacrificed in a demonic ritual. Ciel ordered him to slay his abductors. This marked the beginning of their contract.
Sebastian, in hispast, engaged in "messily sampling every dish available," and has since resorted to only consuming "high-quality" souls. As a result, he is, starving, but firmly holds to the belief that the dinner will be that much better the hungrier he is