Kyle Katarn is a human male from Sulon, a moon of Sullust. He was created for the LucasArts first-person shooter Star Wars: Dark Forces (1995), and carried through the Jedi Knight games, several novels and a body of tie-in fiction.
The Death Star plans
For a decade and a half, Kyle Katarn was the answer to "who stole the Death Star plans?" A former Imperial officer who defected after learning the Empire killed his father, he takes the mission in Dark Forces and delivers the schematics that make the Battle of Yavin possible. Rogue One (2016) replaced that account entirely in current canon with Jyn Erso and Rogue One squadron.
From mercenary to Jedi
What made him interesting was the reluctance. He discovers he is Force-sensitive well into adulthood, treats it as an occupational hazard rather than a calling, and flirts with the dark side in a way the games actually let the player choose. By the New Jedi Order period he is a Master and an instructor, which he is visibly uncomfortable being.
Legends only
Katarn is entirely Star Wars Legends. He has no canon equivalent, and the events of his signature story now belong to different people. He remains one of the most frequently requested returns among long-time readers.
Reading note
He is also a useful case study in how the Expanded Universe worked: a character invented for a video game who became load-bearing continuity for fifteen years, because nothing else had claimed the gap he filled.