Columbus asked Portugal's king to fund his voyage. The answer was no. Next, he asked the rulers of?

Answer: King of Spain Ferdinand II and Queen Isabella.

Explanation:

Columbus spent four years trying to persuade the King of Portugal to assist him in his expedition. The king persistently refused him, so Columbus eventually went to Spain.

The Spanish authorities liked Columbus' idea, and his journey was financially supported and approved. He was provided with three ships, the rank of Admiral, and some financial gain from the newly discovered areas.