Xesh is a human male taken as a child by the Rakata of the Infinite Empire and trained as a Force Hound — a dark-side tracker used to sniff out worlds strong in the Force for conquest. He was branded on face, back and arms with the Aurebesh letter Xesh, which is the only name his owners gave him. He gave himself another, Tau, meaning "soul" in his own language, and told nobody except Shae Koda.
The crash
His ship, the Devourer, comes down on Tython in 25,793 BBY, and the Je'daii Order pulls him out of the wreckage. This is the premise of the whole series: a monastic order that has spent millennia balancing Ashla and Bogan — light and dark as two sides of one discipline — meets a man who has only ever been taught one half, weaponised.
Why the series matters
John Ostrander and Jan Duursema built Dawn of the Jedi as the origin story of the entire tradition, and Xesh is the wedge that breaks the balance. Everything the Jedi become — the rejection of the dark side, the fear of attachment, the eventual schism — is presented as a downstream consequence of the Force War his arrival triggers. It is the most ambitious piece of ancient-history worldbuilding Star Wars Legends attempted.
Where to read it
The comics ran in three arcs — Force Storm (2012), Prisoner of Bogan (2013) and Force War (2014) — and Tim Lebbon's novel Into the Void (2013) sits alongside them. The series was cancelled when Lucasfilm ended its Dark Horse licence; it does not have the ending Ostrander planned.