Explanation: The Praetorian Guard were a formation of soldiers/secret police used to guard the Emperor (amongst other bodyguards - Emperors needed bodyguards to guard against their bodyguards, lmao). They've acquired a reputation in the modern day, not incorrectly, for being quick to turn on Emperors and swap sides during civil wars.
'Praetorians' are also a formation of troops in the Warhammer 40,000 tabletop game. They're much more British-colonial inspired, and have futuristic weapons. Whichever Emperor got these fellows will probably last a bit longer than with the other kind of praetorian!