Every elite special operations group has its own storied rite of passage. Navy SEALs undergo a simulated drowning. Green Berets drink snake blood. North Korean special operators do whatever the hell this is.
Such rituals have been an important component in warrior cultures for centuries, and the famed citizen-soldiers of ancient Sparta are no exception. The Spartan are often viewed as among history's most elite warriors, with a culture built to breed and groom the perfect fighting force. Rank-and-file Spartans were trained since birth to be strong, loyal, and ruthless fighters. But a select few were singled out to join the Krypteia — the closest thing the Spartans had to 'special operators.'
Scholars believe that the Krypteia served as the Spartans' reconnaissance soldiers, shock troops, and even military police. As such, their loyalty and commitment to the state was just as important as their skill at arms. And just like today's special operators, the Krypteia had their own initiation ritual. It's believed that in order to complete their training, candidates had to ambush and murder a Helot — a member of the Spartan servant class. Only then, could they prove their willingness to kill in the name of the state.
This video from the American Heroes Channel explains the ritual.