PK-117 is a Promethean Knight. Built by the Forerunners to fight the flood. His one goal was to die but kill as many Flood as he could. But during the middle of a battle, a bright flash of light sucked him away. During the teleportation process, he went into automatic stasis. His system needed to reboot for 1000 years. Lucky for him he will awaken on the day that the Crystal Empire returns. By the way, PK stands for Promethean Knight if it wasn't obvious enough