From the Super Mario Wiki
Kolorado's father, who appeared as a non-living Dull Bones (a sub-species of Dry Bones) in Paper Mario: The Thousand-Year Door, was the father of Kolorado from Paper Mario. Although Kolorado's father is now a Dull Bones, he was once a Koopa.
Kolorado's father is first seen in one of the early rooms of Hooktail Castle in Paper Mario: The Thousand-Year Door, where Koops mistakes his bones for those of his seemingly late father Koopley. Thinking that the rumor that Koopley is dead was finally confirmed to be true, Koops persuaded Mario to read a letter that the skeleton was clutching. If the player chooses to indulge Koops' request, the heroes learn of Kolorado's father's attempt to destroy Hooktail. Although he managed to infiltrate the dragon's castle, he soon found himself "stuck", and expired soon after.
Despite failing to achieve his goal, Kolorado's father managed to learn much about Hooktail's tactics and weaknesses, which he writes down in his letter. He warns the reader that Hooktail tends to feign surrender when weakened, trying to catch opponents off guard by offering gifts in exchange for their mercy. He also claims that the one thing Hooktail fears is something "that begins with 'cr' and ends with 'icket'". The letter is ended with the phrase "My last words go to my son, Kolorado: I love you, and I'm proud of who you've become." As these words were read to Koops, he embarrassingly admitted that these must not be his father's bones after all, and Mario and his team continued onward. Since his bones remained intact and the letter could be read again at any time, Kolorado's father played no further part in the game.