The 1999 Routledge grammar Catalan: A Comprehensive Grammar describes four variations in in Catalan with respect to the personal article:
i) En, Na, N'
ii) en, na, n'
iii) en, la, l'
iv) el, la, l'
These have the following distribution: i) is formal literary written style; ii) is Balearic Catalan; iii) is current in Catalonia; iv) is colloquial Barcelona Catalan. In southern Catalan and Valencian, no personal articles are used in front of names.
The number of people not receiving the personal article (as in, how famous do you have to be) varies between pattern ii) in Balearic and patterns iii) and iv) in Catalonia. In Balearic Catalan, only Biblical persons and those from Classical Antiquity drop the personal article. In Catalonia, any public figure or historical figure can drop the personal article; its use implies a certain familiarity, solidarity, or even approaching a derogatory tone.
So which came first? The same grammar explains:
[..] in many varieties the standard definite article (el, la) has taken over from the original personal article forms.
... implying that the personal articles were the 'original' in front of personal names (dating from the 16th century at the latest), and that the definite articles are a later replacement.
According to the article "On the emergence of personal articles in the history of Catalan" in Cycles in Language Change, the development of the personal articles from Latin domine goes via adjectival elements, which are specifiers; then they become heads and from there into proclitic affixes.
It seems that there is substantial cross-linguistic diversity in the West European Sprachbund when it comes to definiteness vs indefiniteness and proper nouns. This paper suggests that since proper nouns are "by default" definite, extra articles can add other shades of meaning: being de-animated, statehood, familiarity.
It appears to me that Venetian [and, I assume, other Gallo-Italian varieties], Portuguese and Catalan have followed a broadly similar pathway, but with slightly different details. I'm not sure about the case of Modern Greek, but there it is even more mandatory.