1. Edgar Ross
I think everyone knew this was coming. Edgar Ross is the antagonist of the game andthe director of the Bureau of Investigation. Having kidnapped Abigail and Jack Marston, he forced our protagonist into his journey, killing his former friends Bill Williamson and Javier Escuella. Once this is complete, Ross tells Marston that Dutch has reared his head around Tall Trees and it is Johns job to bring him to justice as well. Once Marston has completed his tasks, Ross is unimpressed with Johns inability to have shot Dutch himself, taking John's pistol and shooting Dutchs body, stating that, It looks better in the report. Finally Abigail and Jack are free and John can return to a peaceful life... Until Ross brings an army to kill John Marston! Thus Dutchs gang would be completely wiped out (Ross not considering Abigail as a gang member Im guessing). The all-out assault on the Marston ranch ends with John being unceremoniously executed in a firing squad fashion, as Ross lights his cigar and watches the last few agonising seconds of Johns life.
Although Jack gets the job done three years later, it isnt as satisfying an ending compared to if John would have been his slayer. Ross spent the entirety of the game antagonising John, forcing his journey away from his family. It would have only been right for John to defeat Ross following the completion of eliminating his former gang members, although it would have plunged him into being pursued by Bureau of Investigation until death. And onto the one we wish he had killed...