I searched for both "caesar" and "New Vegas" before asking and didn't find anything, so, apologies if this has been asked and answered before.

In the 2010 video game, Fallout: New Vegas, a tribal leader has taken the name "Caesar" and modeled his tribe loosely after what he'd read about Julius Caesar. He and his followers do not use the pronunciation "See-zer" we use today; instead they call him "Kai-sahr." A few of his non-followers say "see-zer" though.

However, before all this, in the game's lore, there was a timeline divergence in the 1950s or 60s — before that, Fallout's history is identical to ours, so what happened hundreds of years ago for us is likewise true for Fallout. The divergence itself is unclear but is thought to be the invention of the transistor (which never happened for them).

I've heard (and have caught myself repeating) that the game's pronunciation of 'Caesar' is correct (which you can hear close to the beginning of this YouTube video) because all C's back then had the hard sound (like K) and for other historical pronunciation reasons. I've also heard that if you were to somehow meet Caesar (I'm assuming they mean Julius) and unless you caught him on a really good day, calling him Caesar and pronouncing it "see-zer" would be seen as an insult likely to get you crucified.

When I searched for "caesar" on this sub, I saw a lot of interesting questions about Ancient Rome. So I figure people around here know quite a bit about it.