Principal Milder is the principal of Milo's school, and like the majority of Swamp City and Danville residents, she is very much aware of the trouble that follows Milo around.
Principal Milder first appeared in "Rooting for the Enemy" where she was surprised to find Milo at the game, having heard that he had promised Coach Mitchell that he wouldn't attend another game after previous mishaps. After Melissa and Milo explained that the coach had given his okay and announced his belief that their team would lose the game at the pep rally, Milder remarked "Did he now? I need to explain pep to that man."
In "Athledecamathalon", she see Milo's parents dropping off his lunch and Body armor.