Explanation: Didius Julianus was a short-lived Emperor who purchased the position of Emperor from the Praetorian Guard after they murdered the previous Emperor. For obvious reasons, this did not go down too well with everyone who wasn't the small number of Praetorians he bribed. Even more predictably, when a Roman general - one Septimius Severus - marched on him to take the position of Emperor, the Praetorians Julianus had bribed were just as quick to sell Julianus out to the new Emperor in exchange for pardons.
Always remember that men you can bribe can be bribed against you!