"The only child of the Demon King and the most powerful being in the Devildom. He is also president of the RAD student council."
Diavolo is the ruler of all demons, and all who reside in the Devildom know of his name. Although his father, The Demon King, is still alive, he has no interest in the affairs of the three worlds and has since then allowed Diavolo full reign over the Devildom.
As a result, it is taken as truth that Diavolo will be crowned as the Future King of the Devildom. As such, Diavolo has begun strengthening the Devildom's relationship with both the Human World and the Celestial Realm through the exchange program, as he believes that the three worlds should live harmoniously with each other.
Diavolo has layered, red hair with his bangs parted to the left side, tan skin, and pale golden eyes. Like the brothers, he too has painted nails - black, in his case.
Demon FormIn demon form, his hair becomes a brighter red, his complexion turns brown，his horns grow horizontally and curl inward, then ends decorated with gold. He has four bat-like wings that are a deep red and black gradient with gilded tips. He wears a large gold pendant of multiple bat wings with a red jewel in the center that connects to a black and gold embellished choker and two gold chains on the side, and a black-furred shawl over his shoulders. On his arms are six rows of golden triangle patterns, and there are black vertical markings on his torso. He wears black harem-like pants with two gold chains, with a red jewel pendant on each side, and a white cloth with gold patterns in the front.
RAD UniformUnlike the other Devildom students, Diavolo wears a special red RAD Uniform with a blue ribbon accent. He pairs it with a formal black shirt with gold button-down collars as well as a neat white tie with a tiepin underneath.
Human World LookDiavolo has a simple black suit on, with a black shirt underneath it. He also has a dark red coat draped over his shoulder, the color matching his dark red tie.
Despite being one of the most powerful demons in the Devildom as well as the Future King, Diavolo takes on a surprisingly fair and compassionate, if not joyous, attitude at almost all times. However, that is not to say he is a soft or lenient ruler, as even without the threat of retribution from Lucifer, all demons appear respectfully intimidated by him.
Diavolo proves to have much more wisdom than his cheerful demeanor suggests. He shows moments of solemn clarity in which he correctly predicts events that will occur in the future either due to his subtle encouragement or his intentional lack of intervention. He has the ability to tell if someone is telling the truth and has made a rule for himself to never tell a lie.
The goals that Diavolo sets for himself, his fellow demons, and the three worlds at large, appear to be pursued with the utmost best intentions. As evidenced by the fact that so far he has only ever done what he has done with the desire to improve the lives of those he rules over, even if the process is painful.
As he tells MC in Lesson 56, Diavolo grew up very sheltered and isolated. His mother died after giving birth to him, and his father was always very strict with him. He never had the chance to speak to anyone outside the castle until he met Barbatos. After meeting him, Barbatos began to tell Diavolo stories about the outside world, which he liked so much that he asked Barbatos to stay with him. Although this was always refused by Barbatos, Diavolo never gave up. Eventually, he convinced Barbatos to stay by telling him that he would not become the Future King of the Devildom otherwise.
Little is known about Diavolo's past, but his goal has always been to build a better relationship between the three realms. He had met Lucifer when he was an angel in the past and was quite courteous towards him, despite the high ranking angel's contempt for him.
After the Great Celestial War, when the brothers fell from grace, he and Barbatos appeared before Lucifer and a dying Lilith in an area which would later be RAD's colosseum. He offered to help Lucifer's sister if he would pledge his loyalty to him. Then Diavolo had Lilith's soul reincarnated as a human.
Diavolo is the first character to introduce himself to MC when they appear at the student council hall.
- In his very first chat with MC, he explains sending them the wrong sticker by saying Lucifer is the only demon who sends him messages.
- Barbatos mentions in one of his home screen dialogues that Lucifer is like family to Lord Diavolo.
- Diavolo has always wanted to go to Asmodeus's parties, but Asmodeus, for some reason, never invites him.
- His name on Devilgram is "LordDiavolo".
- The demon brothers often warn MC that referring to Diavolo as anything other than "Lord Diavolo" will result in punishment from Lucifer.
- Diavolo's father, the official Demon King, sleeps at the bottom of the Devildom due to his disinterest in the affairs of all three worlds.
- His name is Italian for "devil".
- He hates pickles, as revealed in the chat Diavolo's Natural Enemy.
- In the 2019 Dark Santa Event, he received a Santa costume from MC during the gift exchange.
- His hand appears in the demon card art Quality Time for Two.
- In an earlier draft of the game, Diavolo was a prominent figure in the human world as a CEO of the Richter Hotel Group.
- In the event A Devildom Halloween, it was revealed that his birthday is the same day as Halloween, the 31st of October.
- It's also a custom in the Devildom that demons celebrate his birthday for three days every year.
- There is a folder on his computer named after Lucifer, as stated in the event Welcome to the Bunny Show.
- According to a psychological test that Asmodeus taught Diavolo — who brings it up in the chat Behavior in Love — he has a want to "constantly observe the target of his affections."
- In Lesson 56-18, he tells MC that he's a lover of sweet foods.
From Devilgram Stories
- In The Escorts, Diavolo expresses dislike for the Great Witch Maddi, who wanted to marry him. He had a hard time convincing her to give up.
- His favorite treat is hellfire mushroom rolled cigar cookies, as mentioned in the Devilgram for Lucifer's Melancholy.
- He is neither a cat person nor a dog person, according to Hippity-Hoppity.
- He also states that he likes custard.
- In Memorable Photos, he reveals that because he's lived for a very long time and each year resembled another, he never felt the need to take photos for memories' sake.