As far as a foil for Sixgun goes, the Toshiro Mifune kind of wandering samurai makes the most sense, really. Both are throwbacks to a specific time and place and practice an outdated but effective martial skill.

Or, alternately, if you have your heart set on a magic user you might play off the Southwest setting for him. It'd be interesting to see a Native American shaman or maybe some kind of bruja- assuming either of those characters are played with respect and not as some kind of stereotype. 

Just some musings off the top of my head, feel free to take them or leave them.