Gaius Julius Caesar (; 12 or 13 July 100 BC - 15 March 44 BC), known by his cognomen Julius Caesar, was a Roman politician and military general who played a critical role in the events that led to the demise of the Roman Republic and the rise of the Roman Empire. He is also known as a notable author of Latin prose. In 60 BC, Caesar, Crassus and Pompey formed a political alliance that dominated Roman politics for several years.
The name Gaius Julius Caesar
Using the Latin alphabet of the period, which lacked the letters J and U, Caesar's name would be rendered GAIVS IVLIVS CAESAR; the form CAIVS is also attested, using the older Roman representation of G by C. The standard abbreviation was C. IVLIVS CAESAR, reflecting the older spelling. (The letterform AE is a ligature of the letters A and E, and is often used in Latin inscriptions to save space.)  In Classical Latin, it was pronounced ['ga:.i.Us 'ju:l.i.Us 'kaesar]. In the days of the late Roman Republic, many historical writings were done in Greek, a language most educated Romans studied. Young wealthy Roman boys were often taught by Greek slaves and sometimes sent to Athens for advanced training, as was Caesar's principal assassin, Brutus. In Greek, during Caesar's time, his family name was written Kaisar (Kaisar), reflecting its contemporary pronunciation. Thus, his name is pronounced in a similar way to the pronunciation of the German Kaiser.  In Vulgar Latin, the original diphthong [ae] first began to be pronounced as a simple long vowel [e:]. Then, the plosive /k/ before front vowels began, due to palatalization, to be pronounced as an affricate, hence renderings like ['tSe:sar] in Italian and ['tse:zar] in German regional pronunciations of Latin, as well as the title of Tsar. With the evolution of the Romance languages, the affricate [ts] became a fricative [s] (thus, ['se:sar]) in many regional pronunciations, including the French one, from which the modern English pronunciation is derived. The original /k/ is preserved in Norse mythology, where he is manifested as the legendary king Kjarr.  Caesar's cognomen itself became a title; it was promulgated by the Bible, which contains the famous verse "Render unto Caesar the things which are Caesar's, and unto God the things that are God's". The title became Kaiser in German and Tsar or Czar in the Slavic languages. The last Tsar in nominal power was Simeon II of Bulgaria, whose reign ended in 1946. This means that for two thousand years after Julius Caesar's assassination, there was at least one head of state bearing his name.

Q: Where did the name Gaius Julius Caeser come from?
A: Using the Latin alphabet of the period, which lacked the letters J and U, Caesar's name would be rendered GAIVS IVLIVS CAESAR;
who called him this?
unknown
unknown