memes

Julius Caesar was a Roman emperor who is famous for being betrayed by his council (and possibly son depending how much your read into suetonius's 12 Caesars) and stabbed in the back by like 20 people at the same time. the salad pictured is called a Caesar salad, but it wasnt invented by Julius Caesar it's just commonly attributed to him in meme culture as a joke.

The two answers here are pretty bad, so here's my take as a history nerd.

Gaius Julius Caesar was a highly ambitious Roman politician who through very clever political manoeuvering and incredible military success (considered a military genius) forged a path to almost complete power after winning the civil war and beating the opposing senators, spearheaded by Pompey and Cato. After becoming dictator for life, he was assassinated on the ides of March (the 15th) in 44BC by a group of opposing senators, which included his adopted son Brutus (daughter of his long time lover Cornelia). After the assassination Rome again fell into civil war, with Gaius Julius Octavianus eventually becoming the first Roman emperor, now usually known as emperor Augustus.

Caesar was never an emperor, but the word emperor in many languages is directly based on Caesars name. For example: czar in Russian, kaiser in German and keizer in Dutch.