Henry's Mum, or simply Mum, is a supporting character in Horrid Henry. She is...well, the mother of Horrid Henry, as well as Perfect Peter, and is Henry's Dad's wife. She almost always tells Henry off, mostly due to Peter telling on him due to Henry's torment towards him him. She regularly says, 'Don't be horrid, Henry!' to Henry whenever he's being Horrid, and she usually sends him to his room much like Dad, whenever Henry misbehaves. Unlike Dad, the series didn't reveal her first name. Therefore, it is unknown. She also dislikes Moody Margaret after an incident where Margaret threw Peter in the trash, and Henry revealed what she did.
Henry's Mum appears an an NPC in All Star Smashers. If Perfect Peter gets summoned as an Assist Trophy, and he gets attacked while he's out, he will call out to his mum, summoning her in his place. She will then star KO the opponent that attacked Peter due to their disgraceful behaviour.
Whenever Henry torments Peter, he will often call out to his mum to deal with Henry.