Hooktail

Hooktail is a dragon in Paper Mario: The Thousand-Year Door that has terrorized Petalburg. She ate many of its residents who came to her castle to slay her, like Kolorado's dad and Koops' dad. When Mario, Goombella and Koops came to her castle to obtain the first Crystal Star, the Diamond Star, they were given a clue on how to defeat Hooktail once they found the dead body of Kolorado's father-- Hooktail cannot stand chirping sounds, especially ones that start with cr- and end with -icket.

During the fight it seems Hooktail is defeated, but before Mario and his team can finish her off, she swallowed some of the audience members to replenish 10 of her HP. Once you defeat her completely, Koops' dad will burst out of her mouth, since he's lived in her stomach.

She has two older brothers named Bonetail and Gloomtail. It was not revealed that Hooktail was female until the fight with Gloomtail, who attempted to defeat Mario and his friends for slaying his sister. Hooktail resides in Hooktail Castle, while Gloomtail was in a chamber in the Palace of Shadow, and her (presumably oldest) brother Bonetail was on the bottom floor of the Pit of 100 Trials.

According to Grifty in Rogueport, the three siblings were once the pets of the Shadow Queen.

Later on in the game, when Mario and company revisit Hooktail's lair, they find no trace of Hooktail. Goombella wonders briefly where Hooktail disappeared to, but ends up deciding Hooktail's absence is a good thing.

Trivia

 * In the upcoming Super Paper Mario, there is a dragon boss that is closely related to Hooktail.