What's your name? How do they call you? What is your full legal name? Why do we have two surnames? Do you know that English people only have one surname?
For your information, the ancient Romans used three words (some used four or even more) for their legal name.
PRAENOMEN NOMEN COGNOMEN
The Praenomina were the equivalent to our first name and, curiously, there were only a few dozens first names (less than 40) , such as, Aulus (A), Appius (Ap), Gaius (C), Gneus (Cn), Decimus (D), Kaseo (K), Lucius (L), Marcus (M), Octavius, (O), Publius (P), Quintus (Q), Servius (S), Sextus (Sex), Titus (T), Tiberius (Ti)...
Unlike today, Praenomina were used only in the familiar context and some of them exclusively belonged to particular families, being forbidden to be used by others.
The Nomina showed the gens or tribe to which someone belonged. In times of the Republic Rome there were 35 gentes (=tribes) each one with its particular features in terms of beliefs, economy and cultural aspects, such as, Aemilia (AEM), Claudia (CLA), Camilia (CAM), Fabia (FAB), Horatia (HOR), Papiria (PAP), Suburana (SUB), Velina, (VEL)...
The cognomina expressed the name of a particular family inside the gens. Many families were named after a distinguishing feature (physically, mainly) of the man who founded the family. The cognomina started to be used around the 100 BC, that's why before this date most of the Romans were called with two words. There was a wide range of cognomina with curious meanings: Agricola (farmer), Aquila (eagle), Balbus (stammerer), Cato (prudent), Crassus, (fat), Lentulus, (slow), Lepidus (amazing), Rutilus (ginger-haired).
Sometimes, a fourth name was added, the agnomen, to highlight the glory or the great achievement of a member of the family, hardly ever transferable to another member of the family.