The Pentathlon consisting of running the length of the stadium, jumping, throwing the spear, throwing the discus and wrestling was introduced for the first time at the 18th Olympiad in 708 BC. The Pentathlon held a position of unique importance in the Games and was considered to be the climax, with the winner ranked as "Victor Ludorum".
The modern pentathlon, invented by Pierre de Coubertin (father of the Modern Olympics), was a variation on the military aspect of the Ancient pentathlon. It focused on the skills required by a late-19th-century soldier. The narrative behind the event told of a soldier ordered to deliver a message on horseback. When the horse went down, he was forced to defend himself with both a sword and pistol. He completed his mission by swimming across a river and running a long distance through the woods.
As of the 2012 Olympics in London completion includes shooting (4 laser pistol shooting stops during 3200m run), swimming (200m), fencing (ranking tournament), equestrianism (12 show jumps with unfamiliar horse), and cross country running (3200m with 4 laser pistol shooting stops).
What would the skills of a 21st century soldier look like today? I would say swimming and running are still obvious choices along with shooting. What would we replace fencing and equestrianism with? Some form of hand to hand combat is a good choice and could include boxing, wrestling, taekwondo or judo. I think rock climbing would be a good choice as well as modern conflicts are often set in rugged terrain. Further rock climbing incorporates body weight, power, core stability and grip strength.
200 m swim
The narrative would be a similar daring adventure of overpowering an enemy combatant (and securing their weapon) using hand to hand combat, climbing to a advantageous position, defending that position with a pistol, and finally swimming and running to a more secure position.