The Mayor of Hamelin is the main antagonist from the Silly Symphony short The Pied Piper.
The Pied Piper
With his town plagued by swarm of rats, the Mayor of Hamelin offers a bag of gold to whomever can rid the town of the rats At that moment, a colorfully dressed young man (the titular Pied Piper) passes by and upon hearing the mayor's decree, offers his services. By playing his pipe, he hypnotizes the rats and leads them out of town where he puts them in pursuit of a giant illusionary piece of cheese.
However, upon his return and request for the promised reward, the mayor and people of Hamelin mock him for demanding payment, claiming that the rats left of their own accord while the Piper played on his instrument and give a single coin instead of the entire bag. When the incensed Piper threatens to lead the children of Hamelin away in retaliation, the Mayor dares him to "blow your pipe until you burst" as the townsfolk had locked the gateway after the rats left. To the Mayor's shock, the Piper not only charms the children into following him but enchants the town gate into ripping itself open and allowing the children to leave. As the Piper leads the children of Hamelin into the hills, the Mayor is left to face the wrath of the angry townsfolk.
Once Upon a Time
In this show, the Mayor of Hamelin is replaced by The Sherif of Hamelin portrayed by Doug Abrahams and appears in the third season, worried by the disappearance of the children caused by Peter Pan.