The first 12 Julius Caesar Augustus Tiberius Caligula Claudius Nero Galba Otho Vitellius Vespassian Titus Domitian
"Caesar" was simply part of Gaius Julius' name. It only became a title after his death. In that way you could say he was the first "Caesar", but there were others of the same name before him - including an ancestor who struck coins bearing the name "Caesar". Octavian took his great-uncle's name and was known as Caesar - as Emperor, his full name became Gaius Julius Caesar Octavianus Augustus.
The 12 Caesars is a reference to the writings of Suetonius in which he included Julius Caesar. However, the first person to use the title "Caesar" was Augustus.
Caesar was treated as a family name by the first four Caesars who were all either descendants of the male Julian line or adopted into it (Julius Caesar, Augustus, Tiberius and Caligula). After the assassination of Caligula the male Julian line died out. When Claudius took up the name Caesar he was making the definitive break from the use of Caesar as a family name to using it as an official title. I’ll take the opportunity to post my new Claudius. The innovator himself.
I just posted this one in another thread, but here's a "Caesar" a couple of generations before "the" Caesar. In fact, this one's even a "Julius Caesar" -- more specifically, Lucius Julius Caesar (c. 134-87 BCE). But that was before Caesar was a title, so it was just his name. It didn't become a title until after his ... great-nephew (?) ... "the" Julius Caesar (100-44 BCE) had taken over Rome: One might say that "Caesar" started to become a title when it was adopted by Octavian/Augustus as his claim to power (well, Julius Caesar adopted Octavian/Augustus, who took his name). Technically, though, it didn't become a legal title until 68 CE after the end of the Julio-Claudian Dynasty, when Nero died. (Since it had to passed along to a non-heir.) So, I would say it was a process with some important intermediate steps. As you seen on the reverse of Augustus' denarius, Caius and Lucius were "Caesares" too. But died before taking over the big show. (That was always kind of a pattern among the Roman rulers. They needed lots of backup heirs.)
And this is the last Caesar. I think this German emperor, who abdicated in 1918, was the very last one to claim the title of Caesar (spelled in German Kaiser).
Germanicus als (adopted) son of Tiberius as well as Tiberius´ (natural) son Drusus junior were "Caesars" by their name, Julio-Claudian family, and status as presumptive successors of the ruling Emperor.
