From Muppet Wiki

King Rupert the Second is a modified version of King Goshposh, as seen in The Frog Prince A full-bodied variation of the earlier fairytale monarch, King Rupert has a fringe of white-hair and lacks Goshposh's ubiquitous cigar. Otherwise, the voice and personality are nearly identical.

The king is the father of Princess Melora and the son of King Rupert the First. He was also very gullible, believing many of Taminella Grinderfall's lies, such as her claim to be his sister. He also mistakes frogs for toads. The king retires, after many happy years "as a scheming despot."

The puppet was recycled as the titular King in "The King's Breakfast" sketch from The Muppet Show episode 121.