Bonanza was an American western/cowboy television series which aired on the NBC television network from September 12, 1959 until January 16, 1973. The pilot episode was written by David Dortort, who also produced the series. Dortort's other creations include The Restless Gun, The High Chaparral, The Cowboys, and the Bonanza prequel, Ponderosa. Bonanza was the first hour-long network television series filmed in color. For most of its 430 episode run, the main sponsor of Bonanza was Chevrolet and the stars occasionally appeared in commercials endorsing Chevrolet automobiles. All of the regular cast members had appeared in numerous stage, television and film productions before Bonanza, but none was particularly well-known.
In 1959, the series was aired on Saturday evenings, most typically a social night. It was soon targeted for cancellation, but given one last chance. A move to Sunday nights at 9:00 PM, caused the series to soar, and it remained high on the Nielsen ratings until Autumn 1972. The Sunday time-slot was crucial to the success of the show: from 1964 through 1967, the show was #1 in the yearly Nielsen ratings. The series was moved to Tuesday nights during its 14th and final season. In terms of longevity, the show remains NBC's second longest-running series, after Law & Order.