The Egytians. They specially mummified their dead rulers, and other people they just put underneath the sand, letting the desert naturally mummify the dead. The pyramids were built to put their dead rulers in.
Fun Facts! At some point in time, they moved some of the mummies from the pyramids and put them in a cave to stop robbers. That's also how they found unknown man E. King Tut was one of the few that was not moved from his pyramid.