"Ciro" is "Cyrus" from Cyrus the Great in both Portuguese and Italian (although with very different pronunciations), thus doubly appropriate given that Ciro Santilli was born in Brazil, and has Italian ancestry.
After he conquered Babylon in 539 BC from the hands Neo-Babylonian Empire, Cyrus the Great did a great service to the Hebrews by allowing war prisoners that were held in Babylon to back to their home Judea, thus terminating the Babylonian captivity. These Jews were imprisoned because they had previously fought a war or revolted against the Neo-Babylonian Empire and lost. As Wikipedia puts it:
According to Isaiah 45:1 of the Hebrew Bible, God anointed Cyrus for this task, even referring to him as a messiah (lit. 'anointed one'); Cyrus is the only non-Jewish figure in the Bible to be revered in this capacity.
He is therefore viewed extremely positively in the good old book. Ciro was quite happy about this name choice by his father, given the human rights connotations of the figure and Ciro Santilli's self perceived compassionate personality.
Particularly fun things related to modern Cyrus are:
Because it belongs to some relatively obscure character of the Bible, the name it has been mostly passed on by writing to every single Christian country, and every single language came up with different way of saying it, because the only place they would possibly hear that name said out loud would be in Church!
As of 2020, the country in which the name is most popular in undoubtedly Italy. In Brazil, it is definitely not common, but also not completely unheard of either, e.g. Ciro Gomes is a notable Brazilian politician.
And Ciro responds to all the versions of the name that he knows of. These include:
  • English:
    • direct English reading of "Ciro" as "See Roll". Not the most cultured, but its what things tend to converge to, especially in highly international environments where it would be impossible to try and learn the origin of everyone's name! So it's fine. Slightly too close to "zero" for comfort.
    • Cyrus, the actual English version of the name. Ciro was so happy when his elderly English neighbour who went to Eton college, upon recognizing what Ciro was, immediately said: "Ah, Cyrus the Great!" He was the cutest, and he had some culture. Many/most English speaking people can't or won't be very sure about the spelling, but the sound of the name has a distinctly exotic feel to it, and the sounds are immediately recognized without sound ambiguity (unlike Ciro vs Zero).
  • French:
    • direct French reading of "Ciro" as "See Rho" with accent on Rho. This sounds exactly like "Sirop", i.e. Syrup in French, which can be good or bad depending on how you look at it.
    • Cyrus, the actual version of the name in French. Similar remarks to those of English apply.
  • Portuguese: "See Ru" with accent on See, and rolling r, and very weak "u". Some people might have some doubt of how to spell it and will ask for confirmation if needed, though many/most will get it right. Not particularly exotic like it is for English speakers.
  • Italian: "Chee Ro" with accent on Chee and rolling r. Widely understood and correctly spelled, more than in any other language. Not exotic at all, could be any random dude from Naples.
    • "fratm Ciruzzo": reserved for the Napolitan mates. It means "my bro little Ciro" in Napolitan. The "m" in fratm is a possessive inflection ("my", "mio", but on the same word), and "frat" is of course something like he standard Italian fratello (brother).
  • German: Kyrus. Because Cyrus the Great is known Kyrus II. (Cyrus the Second, his grandfather was also called Cyrus), Ciro once joked to a German friend that he should call him Kyrus III! He liked that.
and glad to add any new ones as they come.
  • Persian (spoken in 2020s Iran): something like Kurush. Likely the closest sound one to the original, though not sure how certain we can be of this.
He is actually quite happy when people use the name in their own language, because that means they understand the origin of the name.
Some Ciro's of interest:
  • ciros.com is a reference to the possessive "Ciro's", as of 2022 a cute family-held Italian restaurant in Texas, i.e. "Ciro's restaurant"
    • More notably perhaps, Ciro's was the name a nightclub on Sunset Boulevard
    Figure 1. Neon Sign from Ciro's night club (1955) Source.
  • it is unclear if the usage of Cyrus in family names, e.g. the dread Miley Cyrus. www.houseofnames.com/cyrus-history mentions it may be of Greek origin.