The Crimson Guard were, during the Galactic Civil War, a small group of ruthless individuals whom did Emperor Palpatine's personal bidding. Their leader, Captain Vex Salder, had founded the organization after working his way up in the Empire's ranks. The group was stationed to the east of Keren, Naboo, for half of the Galactic Civil War. Their members wore a full suit of crimson Composite Armor into battle. Vex's armor, however, reflected on his personal status in the Empire - a Royal Guardsman.
After the Battle of Endor, the organization eventually was disbanded, in favor of more cost-effective substitutes within the Renmant's elite stormtrooper division, and eventually the members either disappeared, resigned their ranks and affiliation with the Crimson Guard completely, or died off.
Vex was believed to be the last of this fallen group of warriors.
However, when Vex met with Keldon Tyfus, and was offered a position in the Shadow Imperium, the former Royal Guardsman accepted the proposition, under the sole condition that the Crimson Guard be reformed. The former Grand Admiral agreed, and Vex began the recruitment process. Among the members he found were Kakon, a Kajain'sa'Nikto, whom he taught everything he knew. Shortly before Ilan Garuda discovered the Shadow Imperium, Kakon resigned from the Crimson Guard ranks, in interest of recreating the Morgukai Warriors. He left with Vex's good graces.
Along with a mere handful of others, Vex successfully recreated the dreaded Crimson Guard, which served the Shadow Imperium and, for a time the reborn Emperor Palpatine and his Empire. When Palpatine was killed by Damascus, the Crimson Guard saw the Imperium as the "last true Empire," going so far as to be willing to die for the goals and achievements of the organization.
When Darth Trayus arrived and attacked the Shadow Imperium and Sith Brotherhood, the Crimson Guard was ordered by Tyfus to remain on Testria. The order proved to be practical, as the fighting ceased with the death of Ilan Garuda. Afterwards, Trayus and Sidon Kun visited Tyfus, and offered him a position as a staunch supporter in Trayus's campaign. Tyfus reluctantly agreed, and soon found Trayus taking over the Shadow Imperium and turning it into the Crimson Empire. Tyfus was the first to, reluctantly, swear loyalty to Trayus, and the Crimson Guard were reassigned as his personal bodyguard.
The new assignment did not sit well for Vex Salder, who began to question Tyfus's motives, and the position of the Crimson Guard under his employ. Through the unfolding events of the Shadow War, he watched carefully Darth Trayus's maneuvers and motives until, not long after the Battle of Arcanix, he pulled his fellow Guardsmen away from the Crimson Empire and fled its territories to Yinchorr. There, the Guard holed up in the abandoned Royal Guard Academy, making it their headquarters as they worked on figuring out their next move. Vex also opted to begin the Crimson Guard's training to be far more akin to that which produced the members of the Royal Guard, hoping that, with this added benefit, they could make a stand against whoever managed to find them.