The mule is the most common and oldest known hybrid. It comes from breeding a jackass (male donkey) and a female horse (mare). The mule has been deliberately bred by man since ancient times.
Here are the advantages of a mule over a horse: mules have much harder hooves, better suited to cover rocky terrain, easier to train, can travel longer distances in a day, only need four or five hours of sleep, live longer than horses, and they have amazing strength and endurance.
Mules led to the creation of the U.S. space program. Teams of mules pulled the first jet engine to the top of Pike’s Peak to be tested.