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“I appreciate that, Murphy! They ARE nice eyebrows.”
Kroop is a Koopa Troopa and the mayor of Petalburg. He is an elderly Koopa, and, as such, has much life experience. This experience serves him and the citizens of Petalburg during times of peace and during times of crisis. Kroop has large, bushy eyebrows, a wrinkled face and green skin.
Kroop's hearing is not what it used to be. As such, the old Koopa calls Mario by the name "Murphy" throughout the plumber's adventure. Kroop also had a trouble in the game. He wanted someone to talk to him. After Mario listened to his long speech, Kroop rewarded the plumber with a Turtley Leaf.
Kroop had a wife in his past. She is only necessarily brought up when Mario first enters Kroop's house. After this entrance, Kroop (who seems to be afflicted with bad eyesight) swiftly "identifies" Mario as a thief. After some ramblings, he eventually tells Mario that he can take any of his belongings; everything but his "pictures of him and the missus." After this is stated, he begins trailing off about memories before quickly getting back to the point.
Later on, if Mario was to accept Kroop's trouble, the elderly Koopa would mention "dating the missus back before she was the missus." Apparently, his wife's father was very strict, always requesting that Kroop's wife be brought home before sundown. As such, on dates, Kroop would constantly watch the sun (even more so than he did his date), which was "kind of blinding, in a painful sort of way." He would also mention that he first told his wife he loved her (apparently by stating something about her shell in a loud voice) on a boarding platform as she left on a nearby train; situations such as this happen to be a movie stereotype, as Kroop himself notes. Before ending his long conversation with Mario, he would also talk about how he and his wife were madly in love and about how his wife used to comb his eyebrows in a tender manner that he enjoyed.
Like all implied characters, little is known about Kroop's wife. Due to Kroop's protectiveness of his pictures of her and his profound love of his memories of her (as well as the fact that she never appears in any other form in the game), it is quite obvious that she is dead. Kroop also has three pictures set up in his house, and, while these are possible candidates for his "pictures of him and the missus," it is hard to make out what they depict (if they even depict anything in particular at all).
Names in other Languages
Note: He is named ハナハナ村の村長 (literally, "Petalburg Mayor") in the Trouble Center list in the Japanese name of Paper Mario: The Thousand-Year Door. The US version says "Mayor Kroop".