Mayor Humdinger can be grumpy at times, seen when he lost in "Pup Pup and Away" and Mayor Goodway/Adventure Bay won. He argues a lot with Adventure Bay's mayor, and he will do anything to be "on top". But underneath, the mayor can be humble and kind.
Mayor Humdinger is rather conceited, thinking that his town is better than Adventure Bay in every way possible. In Season 1, while antagonistic towards Mayor Goodway, for the most part, he played fairly due in part to confidence in his record of winning and generally being undefeated in most of the competitions he participated in, only to end up losing to Mayor Goodway and the PAW Patrol.
As of Season 2, he usually cheats in order to win, showing a lack of morality and "win-at-all-costs" personality. He is also the assembler of the Kitten Catastrophe Crew, a group of mischievous cats who perform heinous deeds to support his efforts. He has also become slightly more villainous in Season 2 (whereas in Season 1 he was simply antagonistic) to the point he and the Kitten Catastrophe Crew have their own secret lair and he behaves more like a stereotypical villain such as laughing maniacally and even covertly observing the PAW Patrol via a video monitor ("Pup-Fu!"). He is also shown to be willing to resorting to stealing something he wants, such as Wild Wilbur's hidden treasure ("Pups Save an Outlaw's Loot") and Farmer Yumi's priceless Martial Arts scroll ("Pup-Fu!"). He is also shown to be quite greedy in "Pups Save an Outlaw's Loot". However, his plans can occasionally backfire due to his own overconfidence and lack of forethought, resulting in him needing to be rescued by the PAW Patrol.
In "Pups Save a Snowboard Competition", he is shown to care about Cat Rubble and Cat Chase when they are in danger of falling off a cliff, as he is shown nervously biting his fingernails, though returns to his usual self once they are safe and reluctantly thanks Ryder and the PAW Patrol due to his pride, but ends up thanking them albeit begrudgingly.
In "Pups Save Friendship Day", his competitiveness is so great that he is willing to turn a holiday about friendship into a contest between Foggy Bottom and Adventure Bay. He is also shown to be slightly narcissistic as he called a Friendship Day Cake that resembled him the most beautiful thing he had ever seen. He was also touched by Mayor Goodway's attempt to help him when he was being carried away by his balloon bouquet and promised to try to be a little nicer. However, his later appearances show that this didn't take and he continues to be villainous.
He is a rather poor judge of character. He trusts his nephew Harold, even though the latter often betrays him.
Mayor Humdinger has dark brown eyes, light peachy skin, and blonde hair. He also has a big bushy blonde curled mustache. He wears a blue top, purple pants, brown shoes, and a blue top hat. His standard outfit resembles Rich Uncle Pennybags (the Monopoly man).
He also looks similar to the statue of Mayor Goodway's Grover Goodway.