What was the name of the ruler of the Land of Make-Believe?

The ruler of the Land of Make-Believe was King Friday XIII.

King Friday XIII is the imperious monarch of the Neighborhood of Make-Believe in Mister Rogers' Neighborhood. Fred Rogers performed the puppet character in the original series, giving him a grand, theatrical personality filled with formal speeches, elaborate vocabulary, and royal commands.

Despite his title, King Friday is not always wise or calm. He can be egocentric, stubborn, irrational, and resistant to change, but he is also capable of listening when other residents explain why he is wrong. His name is part of the show's playful use of days and numbers: his wife is Queen Sara Saturday, and their son is Prince Tuesday.

A common mix-up is confusing the king with Queen Sara Saturday, who later became his wife after first appearing as a commoner from Westwood. King Friday XIII was also one of the earliest puppet characters associated with Fred Rogers, having appeared on The Children's Corner before Mister Rogers' Neighborhood.