King frog

 is a boss the Bearded Man fights in the introduction of Enemy 585. 5. At the beginning screen of the game, the King Frog is holding the Princess and the Princess's dog captive. When the Bearded Man enters the room to where they are being held captive, he jumps over the King Frog and lands on a button behind the King, collapsing the bridge the King Frog is standing on, causing the King to plummet into the lava below. The Bearded Man, Princess, and Guard Dog then escape the Frog King's castle.

Castle
The Frog King owns a castle, which is seen on the first level of Enemy 585. There is also one castle per world. The kings statue is in every castle so every castle is controlled by the Frog King.

Trivia

 * statues are seen in platforms. King Frog's face is also seen on banners in the game. Also, when the player completes a level, King Frog's face is seen.
 * King Frog is obviously based off Bowser, his castle based off his castle from the Super Mario series.
 * The battle between King Frog is very similar to the final battle between Bowser and Mario in Super Mario Bros.