That's a good question. Google seems to think the answer is Severus Snape , but duckduckgo gets what I think is the right answer: Sep Sev. Here's what wikipedia says at the moment: Not much of an authority though. Coin collectors would dispute the "rarely" for Severus II, and I've never heard of Caracalla referred to as "Severus Caracalla." (Though apparently he gets the "Severus" on a few provincial coins.) Also on Wikipedia, the Severus II page: A search for "Severus I" (in quotes) on Google scholar yields no hits. OK, I take it back, it's not a good question. There was no Severus I!