regalman
Reckless Dolphin
Capital has an "x" in it 

Nope!
The leader was famous after death, and wasn't a good leader before that.
Wait: I cant think of any capital that has an English X in it. Is the clue in English, or is it in another language, say Greek?
Xacitarxan
A bunch of pre-Columbian Mesoamerican cities as well, some of which were capitals of rivals to the Aztecs.
No, but I think its Armenia, led by Artaxias I, with Artaxata as its capital.
Mesoamerican civs probably wouldn't control Byblos though...
oh yeah, he actually expressed an interest in making a herod civ on jan's stream onceHmm maybe Herodes ?
Could the mystery civ be the Ptolemaic Kingdom under Ptolemy Soter (capital city being Alexandria)?
Regalman hates him so sadly no.