In "The Masque of the Red Death" whom does Prince Prospero invite to his Abbey?

Prince Prospero invited a thousand of the wealthiest people in his kingdom to his abbey.

Prospero has a problem.  His people are dying.  There is a horrible disease known as the Red Death that is killing his people off in droves.

When his dominions were half depopulated, he summoned to his presence a thousand hale and light-hearted friends from among the knights and dames of his court, and with these retired to the deep seclusion of one of his castellated abbeys. 

These courtiers would have been the most important people in the kingdom, and the people with the most money.  They all just hung out together and had a good time while back home people were dying.  Prospero did not care. As far as he was concerned, it was better to have one big party with your friends than take care of your people.

It is not enough that they are holed up in the fortress of an abbey with all they could ever need, far away from the pestilence.  Prospero decides to throw a spectacular ball to celebrate their continued existence there.

It was toward the close of the fifth or sixth month of his seclusion, and while the pestilence raged most furiously abroad, that the Prince Prospero entertained his thousand friends at a masked ball of the most unusual magnificence.

This turns out to have been his fatal mistake.  Half of the people in his kingdom died, and his response was to run away.  Now six months have passed and he and his friends are still alive, so he is throwing a party.  Prospero did not invite Death, but Death came uninvited.  Prospero and all of his friends were living on borrowed time, and they found out the night of the ball.

Leaders have an obligation to protect their population.  This extends beyond favors for the rich.  This story is a cautionary tale against greed and excess, but also against delusions of grandeur.  Prospero thought he could cheat Death.