Mushroom King

The Mushroom King, also known as King Toadstool or "King Bowser", is a seldom-seen ruler of the Mushroom Kingdom. He is a figure that is absent in the video game series, where the princess is depicted as its current monarch. However, he has appeared in other early media.

Super Mario Bros.
In the NES instruction booklet of Super Mario Bros., the Mushroom King is briefly mentioned in passing as the father of Princess Toadstool. With the exception of Super Mario Bros. Deluxe, this is not included in subsequent releases. This is due to the fact that no Japanese manual mentions him, and his hinted existence was invented by the English localization team.

Nintendo Comics System
In the Nintendo Comics System, King Toadstool is Princess Toadstool's father and the de facto leader of the Mushroom Kingdom. However, he is depicted as scatterbrained and dimwitted, so his responsible daughter often performs his royal duties in his stead.

Based on his role, it is likely that he was based off the Mushroom Kings from Super Mario Bros. 3 as he plays a similar role in the comic strips (having a Magic Scepter that is often taken by Bowser's forces and being transformed into various animals).

Super Mario Bros. Film
King Bowser (not to be confused with the actual President Koopa) appears as a main character in the Super Mario Bros. film as Daisy's father and the overthrown king of Dinohattan. He had been de-evolved by President Koopa into a giant sentient fungus that had spread across the parallel world to obstruct Koopa's construction projects.

He continually aids Mario and Luigi throughout the film in their quest to defeat Koopa. Once they successfully do so, King Bowser reverts back to his human form and exclaims, "God, I love those plumbers!"