From imdb:
"Filmed in Spain on a miniscule budget while William Shatner was on hiatus from playing Captain Kirk on "Star Trek" (1966), this film features him playing the dual role of half-breed twin brothers in the Old West."

"Johnny Moon: Next time, don't eat the peyote."

"Johnny Moon: Notah is well-named... his liver is white, like his Yankee father... his heart burns blacker than the skin of his Comanche mother. He's white-bellied, like his name..."The Snake."
Notah: Notah's brother talks like the white man he thinks he is. He's afraid... to be Comanche."

This is truly amazing. I did not realize that Shatner had a performance of this magnitude in his oeuvre.