Pernell Roberts as Sam Boonebr - All of the following would later guest star in Bonanza: Karen Steele, James Best, Lee Van Cleef, and James Coburn. br -David Dortort [creator of Bonanza] discovered Pernell Roberts when he was working on the stage at Universal Studios. He saw Pernell in the newly released "RIDE LONESOME" film and was highly impressed with him as well, and so.... Pernell was in the "Cast Of Bonanza as Adam Cartwright".