The ancient pentathlon was designed to test a soldier's skills. In the early 20th century, the modern pentathlon was invented to...test a soldier's skills. Except the soldier they had in mind was a cavalry officer trying to get back to his people after being trapped behind enemy lines.
Thus, the modern pentathlon consists of five events - shooting, fencing, swimming, running and riding.
Except that the modern pentathlon adds a twist to the riding segment. The competitors do a fairly standard show jumping course which is generally easier than other Olympic courses. The twist is: They have to ride a completely unfamiliar horse. (The idea was that it would test a cavalry officer stealing a horse to get away). Competitors generally meet their horses 20 minutes before the event and get time to warm up. This can make modern pentathlon quite, uh, entertaining to watch, especially as competitors tend to spend more time training for the other events.
The horses are generally provided by local show jumping trainers and are drawn randomly.
Some uh...moments from Rio. (Over the fence without the horse, and the horse leaving the premises, for example).
As a rider, riding an unfamiliar horse can be challenging and there's only one thing worse:
Riding a horse you already know hates you.