Leaving aside monarchies as Britain, Saudi Arabia, and arguably Best Korea, where wealth comes from governing: in any country it is impossible to become a ruler if you are not rich. Maybe not born rich but middle class if you get a good party, which are themselves rich before you, to nominate you (Macron in France, arguably Obama in the USA). But poor people don't become rulers. Exceptions are rare and generally have mitigating factors: the first Kim in Best Korea (peasant) had foreign support; Morales in Bolivia (peasant) and Lula in Brazil (blue collar factory worker) spent many years organizing widespread social movements; Maduro in Venezuela (public transportation bus driver) free rode from Chavismo's rule. I don't know the exact background of Zelensky or how much or how little he is related to Ukrainian corruption, which would increase his access to wealth even if he didn't have lots of personal wealth, but that he was a TV star before politics already tells me that he, even if he started poor, had already got reasonable access to money and fame.
Manny Pacquiao faced abject poverty as a kid. Now he is in politics. Some think he has a good shot at eventually being President. All of this happened not directly from his poverty but after becoming very rich and famous through his boxing.