King Toadstool, also called The Mushroom King or The King of Mushroomland, is the King of the Mushroom Kingdom and the father of Princess Peach. He is notable among the Super Mario characters in that he is mentioned in the storyline provided for the Super Mario Bros. instruction manual, but has never actually appeared in any of the games.
King Toadstool was prominently featured as a regular character in the Super Mario Bros. comics published as part of Valiant's Nintendo Comics System imprint. In the comics, the King is very dimwitted, to the point that, in the story "Duh Stoopid Bomb!", the titular Stupid Bomb is shown to have no effect on him. He appears to be based off of the Mushroom World Kings from Super Mario Bros. 3; in two stories, "Mutiny on the Bouncy" and "Piranha Round-Sue", the King is turned into an animal (a dog in the former and a chameleon in the latter) and sends Mario to find a magic wand in order to change him back.