To begin with, “Caesar” was a family name. Now, in various forms, it is a generic term for “ruler” or “emperor.”
In Roman naming practice, a newborn child was given three names (tria nomina). The praenomen was a name like Lucius or Marcus. The second name was the name of the tribe, clan, or gens, such as the Julii or Cornelii. The third name was the cognomen, a nickname that distinguished one branch of a gens from another. Sometimes an adult would adopt a fourth name called an agnomen. This was a nickname he had earned himself.
Caesar was the cognomen of the family to which the dictator Gaius Julius Caesar was born. Its origin has been explained in various ways:
The cognomen “Caesar” originated, according to Pliny the Elder, with an ancestor who was born by caesarian section (from the Latin verb to cut, caedo, caedere, cecidi, caesum). The Historia Augusta suggests three alternative explanations: that the first Caesar had a thick head of hair (Latin caesaries); that he had bright grey eyes (Latin oculis caesiis); or that he killed an elephant (caesai in Moorish) in battle. Caesar issued coins featuring images of elephants, suggesting that he favoured this interpretation of his name. (Wikipeda)
Julius Caesar himself had a receding hairline so another possible explanation is that his family may have carried the gene of male pattern baldness and the nickname “Caesar” (hairy) was ironic.
When Julius Caesar was killed, his nephew, whom he adopted as his heir, took the name Gaius Julius Caesar Octavianus. The Octavianus was his birth name so he kept it. Later on the Senate gave him the agnomen Augustus. That’s the name by which he is known as the first Emperor of Rome.
Augustus and his first four successors were related by blood so they all more or less had the right to the name Caesar. After the death of Nero, however, the Empire was up for grabs. In the chaotic “year of the four emperors” that followed Nero’s death, the name “Caesar” became a synonym for “ruler.” Galba was the first to assume it as a title. (He got to use it for about seven months.)
So famous was the title Caesar that it found its way into all the European languages. It was probably the first Latin word adopted by the Germanic languages to which English belongs.
The Romans pronounced the word with a hard c and that’s how it came into the Germanic languages. If it hadn’t been for the immense influence of Norse and French on English during the Middle Ages, the modern English word for “caesar” would have developed into something like “coser.”
During the time of the close relationship between the English and the Danes, however, the English replaced their own word with the Norse keiser (cayser, kaiser). Then, after the Norman Conquest, when French became the language of the ruling classes in Engand, the French word, with its soft c pronunciation, became the preferred form.
Later on, the word Kaiser came into English again, this time as the title of the German rulers.
The word Czar, which English speakers use to refer to the Russian emperors, entered the Russian language as Tsar, the Old Slavic version of Caesar: tsesari. The spelling Czar is a respelling of the Russian word with the letters of the Latin alphabet. The spelling with cz was common in European languages because that was how it was spelled the first time it appeared in a European book in 1549, but the French adopted the spelling tsar in the 19th century and the London Times prefers it. In German it is spelled Zar.
In the U.S. the word czar is now used to refer to anyone who is in a position of some kind of control. Ex. “Drug Czar” (either a powerful drug dealer OR a government official supposed to combat drug trafficking); “Education Czar.”
Little Caesar (1931) is the title of an historically significant film in which Edward G. Robinson played a gangster and defined the cinematic crime genre.
Such is the continuing charisma of the word that it continues to be used to suggest power and grandeur.
The word’s association with food is probably owing to its Italian origin. (Ex. Little Caesar’s Pizza.) A Caesar’s Salad, however, has nothing to do with the late dictator.
According to the Online Etymology Dictionary, the salad is named for Cesar Cardini, a restaurant owner in Tijuana, Mexico who is said to have served the first one in about 1924.