It is stated that he is 14 years old at the beginning of the story, with the birthdate of November 5th.
His favorite food is Oily fried fish and chips.
Shortly after he was born, Alois had been kidnapped. His mother in deep grief, committed suicide, leaving Alois father to search for him alone. He was made to work as a slave in an unknown village. Something had occured in this village which killed everyone, including Alois's friend, Luca, who he once refers to as his "little brother". Alois was the only survivor of this event.
One day, Alois returned with Claude, and due to his father dying under mysterious circumstances soon after his return, Alois became the Trancy successor, something that his uncle Arnold finds questionable.
SpoilerIt is hinted that there is tension between Alois and his uncle, and that something may have happened in the past to have strained their relationship.
His emotions are quite unpredictable; one of his few consistent traits is his attachment to his butler, Claude, whose he tries to attract his attention frequently. He seems to have an overall cheerful disposition in spite of his hardships and misgivings, making him a sort of foil to Ciel. He seems to have taken interest in having Ciel.
Alois can be easily frightened of things such as: the dark, being alone, adding to his childish elements of his personality. And he is somewhat hyperactive. He also shows signs of sadism and narcissism.
SpoilerAs shown when he gouges out Hannah's eye in the first episode.
Alois also appears to be easily angered and loses interest in things very quickly. He often uses harsh and impolite language, regardless to whom he is speaking to.
His contract mark is held on his tongue and not visible at all times, where as Ciel's contract mark is in his eye and is visible at all times. His contract mark only shows if Claude is nearby.
SpoilerIn episode 8, it was said by Grell that his real name is actually Jim McCain.
His surname is often spelled as "Macken", which is normally wrong while it doesn't exist as an English surname, while McCain does.