Xenex is the home planet of Captain Mackenzie Calhoun, the captain of the USS-Excalibur in the series of novels 'Star Trek: New Frontier'. The people of Xenex were enslaved by the Danteri until Mackenzie, then known as M'k'n'zy of Calhoun, while just a teenager, lead the battle for their freedom.
M'k'n'zy meets Picard some time after overthrowing the Danteri, and eventually goes to Starfleet Academy, and while there changes his name so people can say it.