Lord Pain is a demon-like being who rules over The Plane of Eternal Suffering.
According to his confession to Billy in House of Pain, he was named Charles and came from The Plane of Happy Ponies, presumably temporarily, as The Plane of Eternal Suffering is seen in Everything Breaks. It is possible he renamed the Plane of Happy Ponies. According to a flashback sequence in Wrath of the Spider Queen, he attended Doomsday Junior High in the audience of the auditorium, implying he was around the same age as Grim.
He first appeared in House of Pain. He traveled to Endsville where he served The Grim Reaper faithfully, and even tried to destroy Billy and Mandy in order to free Grim, until Mandy tricked him into becoming her servant instead, since she was the master over Grim, and thus technically the true master.
He later appeared in Everything Breaks as Mandy's servant. He renamed the Plane of Eternal Suffering "Level 9" because, according to him, "it sounded more tourist-friendly". He and Billy destroyed everything in Level 9, and then laid waste to Endsville.
He has tattoos all over his body which originally featured Grim, but later altered to show his devotion to Mandy.
He has pale green skin, a pointed nose, and a long chin that juts out, and possesses an overall slender body build.
He carries a mace and shield, and wears a spiked helmet (which obscures the top half of his head), a red and black cape with the collar folded up, and armor colored various shades of blue.
He shows complete obsession towards "The Master" who at first was Grim, but later was replaced by Mandy. He goes as far as to have The Master's image tattooed all over his body, and joyfully obeys The Master's every command, no matter how degrading the task may be. He shows joy in being in the service of the Master, and begged his first master to take him as a servant, literally on his hands and knees.
He is also highly destructive, taking joy in destroying things, and even caused the inhabitants of Level 9 to move out after destroying parts of the city too often. He even fails to understand why Mandy and Grim are concerned about Billy's destructive habits, surprised that they express their concern "like that's a bad thing." However, he does become angered when Billy destroys one of his statues, suggesting he only tolerates destruction of other people's property rather than his own.
- Lord Pain is believed to be skilled in combat, although he is not shown in combat outside of the video game.
- He is able to speak in the dark forbidden tongue that causes destruction to all mortals within hearing range.
- He is able to open portals between dimensions, like most supernatural beings in the show.
- He is shown changing his size in Everything Breaks, but this appears to only have been for dramatic effect.
He is somewhat friendly towards Billy, and in Everything Breaks referred to Billy as his "breaking buddy" since they like to destroy things together. However, he seemed quite irritated when Billy broke his statue, only refraining from reproaching him because of Mandy's orders.
When Grim was Lord Pain's master, he idolized him, having tattoos of Grim all over his body to show his dedication. He still respects Grim as his former master.
His current Master, he idolizes her, and obeys her every command. He even had his tattoos altered to be in her image, to show his dedication to her. She rarely uses Lord Pain's services in the show, however, and when she does, she usually uses him for trivial things, such as cooking her meals.
- In his original set of tattoos, one of them says "Fear the Reaper" as a possible reference to Blue Oyster Cult's famous song Don't Fear the Reaper
- In Wrath of the Spider Queen he tells Grim to do something that would make him want to tattoo his image all over his body as a direct reference to the events in the episode House of Pain
- When he first appears, Grim does not recognize him, despite them going to the same middle school.
- According to the videogame, the first tattoo he ever got was a dolphin on his left ankle.