This has to be unique in the history of Hollywood. Leading director and screen legend Howard Hawks loved this film so much that they made three variations of the same movie. By the time Rio Lobo was made, the theme was getting a bit thin, but it's still grand entertainment.
The first part of the film is set during the Civil War with John Wayne pursuing Confederates who are stealing army payrolls. He does catch up with them and the Civil War ends. He befriends his erstwhile enemies and asks for their help in locating the informer who was giving them information.
That all sets the scene for the third variant of Rio Bravo/El Dorado theme. Playing the old codger part is Jack Elam who by now had quit being a screen menace and was doing comedy and doing it well. The two younger sidekicks are the former Confederate enemies, Jorge Rivero and Chris Mitchum.
Rio Lobo had the presence of two stars of the Mexican cinema, Jorge Rivero and Susana Dosamantes. Dosamantes played Mitchum's girlfriend and Jennifer O'Neill played the Angie Dickinson part although Wayne was now deciding he was too old for the romance. She pairs off with Rivero.
In a small bit part is Sherry Lansing who left acting soon after Rio Lobo and really hit the big time, going into the production end of the movie business and becoming head of first 20th Century Fox and later CEO of Paramount.
The two principal villains are Victor French who played the neighbor on Little House On The Prarie and Mike Henry who was one of several screen Tarzans.
It's a good John Wayne western and that takes in a whole lot of territory pilgrim.