X6-88 is a villain featured in Fallout series. He was a Courser created by the Institute for high risk missions and Synth retrieval operations.
Created the the Institute, X6-88 was developed for the Courser Program within the Institute. Coursers act as assassins, spies, and occasionally retrieve runaway Synths.
He's first seen in the memories of Kellogg, as he gives the mercenary a mission to hunt down the rogue scientist, Virgil.
He can then be seen at Libertaria after meeting with Father. He's on a mission to retrieve Gabriel, a runaway Synth given new memories by the Railroad.