Sullivan is the adoptive grandfather of Iruma and the principal of the Bablys Demon School. He is one of the Three Heroes, the most powerful and influential demons in society, and is a possible candidate for the new Demon King.
Sullivan is a very tall and imposing figure. He is bald, save for two large yellow horns on the side of his head. He has pointed ears, a large nose, and a white handlebar mustache. A pair of glasses sits at the top of his nose, and always obscure his eyes, despite being tiny. The only exception to this is when his eyes are closed. His fingernails are long and are painted a dark purple.
He wears a dark purple suit with long coattails and a white-furred collar with what appears to be the skull of a large bird in place of a tie or bowtie.
Sullivan is mostly just a silly old man. He is constantly doting on Iruma. Sometimes the situations Iruma gets in because of him are embarrassing or even dangerous, but he never means any harm.
Though he seems mostly happy-go-lucky, Sullivan's high standing is well earned. He has demonstrated his power and knowledge plenty of times, both as a principal and a grandfather. His insights and advice can prove to be very helpful at times. Despite his seemingly benevolent disposition, he does on occasion reveal a more menacing side to his personality, which startles whomever is around him.
Very little about Sullivan's past is known at this point, however it is known that he is one of only three demons alive (Lady Levi, Lord Belial and himself) to have reached the rank of Yod, putting him in the position of possibly being able to inherit the throne as Demon King (or Demon Lord).
A few hundred years ago, when the Demon King Derkila was not missing, Sullivan was a subordinate serving Derkila, the relationship of both seemed very close.
A human child that Sullivan adopted as his grandson, out of loneliness and envy. Sullivan allowed himself to be summoned by a pair of humans in the human world, making a deal for Iruma in exchange for money. He is very affectionate and caring towards him, despite being different species, not blood-related (and kidnapping him). He has a hard time refusing anything Iruma asks for, and often spoils,, pampers and showers him in gifts.
Sullivan's right hand demon, a servant who also works as a secretary of sorts. Opera likely lives in the same house as Sullivan and Iruma, managing the laundry, cooking, timetabling and transport for the two of them. They have a master-servant relationship, with Sullivan relying heavily on Opera's abilities and advice to keep him on track and away from distractions.
The Three Heroes
In chapter 22, it seems that they get along well, although they bicker over who has the better grandchild.
High Magic Capacity: Sullivan has incredible levels of magical power, in terms of both raw output and the amount of magic he possesses.
Teleportation: Sullivan has the ability to teleport.
Time Manipulation: Sullivan has the ability to either slow time to a standstill or to stop time, as he had done in the first episode of the anime, so Iruma doesn't get hurt, and in the nineteenth episode which he stops the fireworks from falling into the school and change the path to outside the school area.
Gravity Manipulation: Lord Sullivan has the ability to manipulate the weight or force of gravity on an object or individual through the use of the spell Fractal.
Despite being a member of the Three Greats, Sullivan is not a Yodh ranked demon in the anime version of the series but he is at the peak of Teth.
Because of Lord Sullivan's High Magic Capacity, he can sense when a high level is being cast, like when Kirio released the stored up energy of his pendent.