|Hold it right there, outlaw!|
This article is littered with spoilers, so I reckon you might ought'a mosey on down the road if you don't want to read any plot details.
Diego is a General of the Mexican Army.
In a flashback told by Sheriff Bartlett, Diego and his army fought a pitched battle with a US cavalry regiment over a bridge crossing the Rio Grande. He ordered his subordinate, Colonel Daren, to prepare the cannons while he and his men held off the first wave. After using flares to highlight the enemy cannons, his artillery batteries knocked out the enemy's artillery support with precise, concentrated fire. When the US cavalrymen continued to assault his position, Diego ordered his men to rig the bridge with dynamite while he personally fended off the enemy soldiers.
After blowing the bridge and ending the battle, Diego took account of captured prisoners, including the unlucky civilian, Griffon the prospector. Originally convinced he was a spy, Griff managed to buy his life back from Diego with the promise of gold.
Red Dead Revolver
Upon learning of the wealth locked in Bear Mountain and Griff's unique position as legal claim holder to give it to him, Diego sealed their new partnership by sending Colonel Daren and some hired goons to kill Griff's partner, Nate Harlow. While Daren succeeded in this task, Nate's son, Red, escaped alive, but not before shooting Daren's arm off. Diego rewarded Daren's loyalty by hiring the best doctors and gunsmiths money could buy to have a shoulder-mounted mortar created as a replacement for the left arm of his right-hand man. Soon after, Diego and his renegade army started mining Bear Mountain's rich gold deposits, using captured Union soldiers as slave labor.
Years later, Diego had taken up residence in an abandoned fort, which he promptly renamed after himself. Using a heavily armed and armored stagecoach and train, he delivered Griffon his half of the Bear Mountain gold, presumably in exchange for Griffon using his position as Governor to ensure the United States Army left Diego alone.
The gold mining operation was interrupted when a fully grown Red Harlow, having learned the part they played in his family's murder, started hunting for Diego, Griffon and all their associates: He intercepted Diego's armored stagecoach and destroyed it. Although Colonel Daren was able to capture Red and imprison him in the Bear Mountain mines, Red's cousin, Shadow Wolf, was able to free him. Together, Red and Shadow Wolf assaulted Fort Diego, resulting in the deaths of Shadow Wolf, Colonel Daren and many of Diego's soldiers.
Despite a head start, Diego was not able to escape Red in his heavily armored train and after a mobile battle on Diego's Railroad, Red disabled Diego's train with a Gatling Gun. Unable to kill Red with his rotating, train-mounted cannon, Diego charged him with his bayonet rifle. Red shot him down, and as Diego lie crawling away on his back, trying to barter for his life with promises of gold, whiskey, weapons and women, Red executed him with a point blank shot to the face.
After completing the level Devils and Angels with an Excellent rating, Diego becomes available as a playable character in Showdown Mode.
- The battle Diego fights over the bridge, the explosive destruction of the bridge and the bridge itself are all reminiscent of a battle scene in The Good, the Bad and the Ugly.
- His mission, "The Traitor", is the only time where the player takes control of an antagonist in a Red Dead Revolver mission.
- During the mission "Devils and Angels" he may shout out while shooting at Red Harlow "Hey tonoto, say hello to my little friend!" which is a reference to the movie Scarface.
- He is listed in Sheriff Bartlett's Journal under the Renegade Army section.