When did the convention of people having a two part name originate? (At least in the West)
Depends. In England, they became more-or-less universal during the 14th century, a development which some credit to the introduction of the poll tax, which required that each individual be clearly identifiable. I suspect that the greater drive to clearly identify individuals was actually the shrinking tax base following the decline known as the Late Medieval Crisis.
ETA: I’m talking through my hat here, of course. I am not a historian, but maybe I’ll irritate one into joining the discussion.
People had two and three names back in Roman times. Gaius Julius Caesar, Marcus Licinius Crassus, Gaius Octavius Thurinus, etc.
Since the Romans borrowed words and customs from the Etruscans, it wouldn’t surprise me if the Etruscans had multi-name names. But I can’t find any information on that.
Icelanders still don’t have family names (there are some exceptions). For example, some years ago, the president was called Vigdis Finboggadottir (not sure of the spelling) which is her first name plus patronymic, standard in Iceland. Her father’s first name would have been Finbog, I believe, the extra -ga being the genitive. I have a friend whose last name is Jonsson. When his father (or maybe grandfather) emigrated from Iceland, his fathers name was Jon, whose genitive is Jons and then the -son was added and adopted as a last name.
We had a graduate student from Indonesia who had just one name and insisted it was her only name. I believe that Megawati Sukarnoputri was really just Megawati and added the patronymic to conform to international expectations (she was, after all, Sukarno’s daughter).
When the population of towns became so large that identification by first name became difficult.
“I say Tom the other day.”
“I thought he had sojourned to get supplies.”
“No that’s Tom the blacksmith, I saw Tom the butcher the other day.”
“How is Tom Butcher doing?”
Glad to be able to help out: Vigdís Finnbogadóttir = daughter of Finnbogi. The -a- is, I believe, a special case when the first word ends with a wovel, it should normally be -s- as in Björk Guðmundsdóttir = daughter of Guðmundur.
At least for England, I’ve been led to believe that the Normans, after their conquest, implemented formal last names. Before then, last names were informal, social monikers that could easily change. For example, Robert the blacksmith might be known as Robert Smith. If another blacksmith named Robert moved into town and also went by Robert Smith, one of them might pick some other feature of themself to call themselves by (or someone else might label him with), for example Robert Short (if they were of short stature), Robert Red (if they were ginger), Robert Church (if they lived near a church), Robert Strong (if they was renouned for their strength), Robert Wallace (if they were Welsh) or Robert Johnson (if their dad was named John).
The example of Lars Porsena suggests that they did. However, he was a king, and so may have been exceptionable in this regard.
However, I believe Etruscan script remains undecipherable, and we have little idea what their language was like, so we may never know what was the general rule for Etruscans. Although, as you say, the Romans borrowed much from the Etruscans, that did not include their language.
The Norse sagas list people with last names, of a sort, from the 11th century and farther back. Patronyms and/or “descriptive” names. Harald Fairhair and all that. Enough non-royalty are mentioned that it’s clear that this just wasn’t for elites.
The genealogies listed in the sagas describe kings like Halvdan Kvitbein (“Whiteleg”) Olavson (640-710). His ancestors, progressively more mythical, have patronyms all the way to their descent from gods. It’s not clear if the individuals going back further than that would have used those names.
OTOH, these weren’t stable last names that got passed down. (Just like in modern Iceland.)
Stable last names, at least in that part of the world are relatively recent. My great grandfather used a patronym. So when he left the old country, he had his original name and arrived in America with another. (His father’s patronym.)
Like…
Eric the Red
Leif Ericsson
What I want to know is when CNN, et al, will stop noting parenthetically that an Indonesian person in a news story is so identified because they “go by only one name.” We get it. We’re wise now.
As for some great Icelandic names to ponder, “Njal’s Saga” is a great source. They’re not all ssons and dottirs, either. There is some interesting variation.
I wouldn’t be so sure of that.
The earliest histories of Rome give us prominent citizens who seem to have been called by a single name: Romulus, Iulus, etc. But as the population grew, the use of two names became more typical, and was the standard convention by the Republican Era.
Even the use of two names did little to prevent confusion. One’s nomen was the inherited name of one’s clan (or gens). The praenomen was more of a household name, used to distinguish one member of a family from another, and not typically used by the public. As a result, most families tended to stick with only a handful of these. If, for example, Gaius Julius had the great fortune to be blessed with a son, it was taken for granted that the son would also be named Gaius Julius. A second son would receive a different praenomen, but the choices would still be confined to a short list of those names accepted by the gens (in the case of the Julians, Sextus, Lucius, or Gnaeus were standard). Girls typically had no praenomen, but were called by the feminine version of their respective nomenes. Gaius Julius’ daughter, therefore, was simply Julia. Should a little sister come along, she, too, would be Julia, but would be distinguished from her elder sibling with a descriptive nickname.
During the Republican era, for a mixture of practical and political reasons, larger families began adding a third name (cognomen). Initially this was done as a means of subdividing larger *gens *into branches, but fairly quickly became a fad among the elite classes. Cognomines often started as nicknames – some less complimentary than others. Common family traits such as hair color (Albus (blond), Rufus (redheaded), Ahenobarbus (bronze-beard)), were standard. Caesar (hairy) or Calvus (bald) continue the hair theme. Cicero, though, translates to “chickpea”, meaning that some ancestor of the great orator was well known for having a prominently placed wart.
As time went on, even more names were added. Many of these were honorifics – An early example would be the Publius Cornelius Scipio who defeated Hannibal was given the *agnomen *“Africanus”, a name that was not passed on to his progeny.
We may not be wise now, but it still seems superfluous. It’s kinda obvious that, if that’s the only name they use in the article, then that’s the name they go by.
In response to the above: In fact, the names were so few that they could often be abbreviated with one letter, and everyone knew what it meant. Caesar’s full name was commonly written C. IVLIVS CAESAR, for example.
You’re considerably overestimating the American TV-news-watching public.
Do tell us more.
Would we be likely to read about someone named EriksTranny or something? 
I don’t know to which classes and nations and time periods this applies to, but in modern (way pre-Nazi) times, many Jews were forbidden to have two names.
Not the West, but in Thailand it was about 100 years ago. I believe King Rama VI (r. 1920-25) decreed it.
In Indonesia, many still have just one name. In fact, I knew one academic who could not get published in international journals, as they constantly rejected him for not giving his “full name.” He eventually made up a surname just for use in publications, then all was well.
Actually, I seem to recall that in Germany, at some point the law made family names mandatory and there were many cases where Jews were forced to take family names, sometimes rather insulting ones invented by gentile officials.
For the most part the quality of the name you got depended on how much you bribed the registrar.