Mad Scientist Wannabe
It's more likely than you think. There's a lot of towns in history created by one man and basically under his control for all time. There's one in particular that read like something out of Orwell's worst nightmares, but I can't remember its name right now.
Of course, don't you know anything about ALCHEMY?!- Twin clones of Ivan the Great
Right here
You mean North Korea?
Mad Scientist Wannabe
No, it was somewhere in the American West.
Of course, don't you know anything about ALCHEMY?!- Twin clones of Ivan the Great
Modern mayors are elected to office, rather than being appointed by a superior or inheriting a hereditary title. If the people of the city he built like him enough, there isn't really anything stopping him running for office and winning repeatedly, indefinitely.
That said, I don't know what you mean by "built a city". Did he fund the construction works? Design the city's layout? Work directly in the build crews? Lay every brick himself? Conjure the whole thing by magic?
Work out what your character did to receive so much credit for the creation of the city, and then we can start thinking about how to make their situation believable.
In at least two TV shows that i like, there was a concept used that i'm starting to consider using myself:
A character of certain significance built an entire city and then serves as its mayor or something afterwards.
From a real world perspective, how would something like this work? What would it take make something like that happen? And if the founder of the city is made mayor, wouldn't that mean that they could be removed from office after a certain period time? How would that even work if they literally own the town?