I may be very wrong so please correct me. I believe that Iago is the Spanish version of James. Santiago means Saint James. Why have I never met a Iago? I have met countless people from or descended from all over the Spanish speaking world. Not one Iago. I asked my mother who was a librarian for over 25 years. She never met a Iago in all her years working with the public. Is the name never used anymore? Is Shakespeare’s influence that strong? Am I just not as observant as I thought?
The “-iago” in Santiago is from the Latin Iacobus, from the Hebrew Jacob, and refers to the Apostle James. With me so far? The Spanish version is San Diego, where **Diego **is the Spanish version of Jacob, i.e. the Apostle James.
So, Diego is really the Spanish version of James/Jacob and is a very popular name. Iago, being a Latin name, not so much.
There’s some Yagos, actually, but like InkBlot said, they’re a lot rarer than Jaimes, Santiagos and Diegos. Many of the Yagos are Yago as a nickname, generally as a way to avoid being “Diego the Son” or “Santiago the Third” (which would stem from a classroom/job/group of friends situation, rather than from being Santiago-son-of-Santiago-son-of-Santiago). Another common nickname, but one which applies to Santiagos only, is Santi; in one of my classes (40 and co-ed) we had Santi, Santiago, Yago (who would have been Santi III otherwise) and there was another Santiago in a different class group who was “the lone Santi.”
Would James/Jacques/Giacomo/Santiago/Diego/Jacobo/Jaime/Jaume/Jamie/whatevertheheck be the New Testament name with most divergent renditions in the modern European languages?
I know someone called Jago, but he’s English, not Spanish.
Well there’s John/Jean/Jan/Johann/Hans/Giovanni/Ian/Juan/Jehan/Johannan/Sean/Shane/Yannis /Zane/ Jaenda/ JJenkyns/Jennings/Jens/Jense/Jentz for starters.
John has got to be close.
ETA - scooped! But I didn’t fuss with naming any, so you win.
You can get John/Johan/Johannes/Hans/Hanns/Jan/Jens/Hannes/Jöns/Johnny/Jon (plus possibly some more variants and pet forms) in Swedish alone.
Where does Jaime fit into this?
No. Diego is the Spanish version of Didacus. The superficial similarity of Sant-Iago and San Diego has led people to spout this bit of misinformation quite a lot. Authoritative Cite.
Don’t forget Hamish!
Um, Doc, AFAICT your cite doesn’t actually support your position, if I’m correct in thinking that your position is that “Diego” is not etymologically derived from the same origin as “James”.
So the cite seems to be saying that “Diego” does in fact “perfect the bastardization” (which means, I presume, “produce a variant form”) of the original “Jacobos”, and hence is etymologically related to it.
I think a clearer cite would help, as I confess I don’t quite see how all the statements in that one can be reconciled. This cite seems to put it a little more comprehensibly:
Kimstu, my cite says “Therefore it cannot be said that Diego is either a Spanish or other linguistic form of James.” I don’t see how it could be clearer! The hint is calling the other side “apologists” and saying that they “err.”
Iago is also the Welsh form of James (pronounced ya-go, not ee-ah-go). I always wonder if Shakespeare knew that.
I don’t quite understand that “authoritative cite”.
It seems to me that the second and third paragraphs demonstrate only that Didacus is not the equivalent of James or Jacob, not that Diego is not. And Didacus is the name given to this saint because he studied the Διδαχη των δωδεκα αποστολων (“Didache ton dodeka apostolon”, “Teaching of the Twelve Apostles”).
Perhaps Didacus and Diego are etymologically related. But I don’t think that page presents any compelling evidence of that.
Added in preview: like Kimstu said.
Apropos of nothing in particular, but Kimo is Hawaiian for James.
But your cite also says that the other side’s “arguments are elaborate and extensive, based on a partially correct etymological and philological analysis demonstrating how San Diego perfects the bastardization of Santo Yago, Santo Iago or Santiago”.
Where your cite claims that its opponents “err” is “when they push their linguistic and etymological analysis claiming that Santiago […] is Didacus in Latin”.
In other words, in this sentence your your cite is whanging on the other side for saying that “Santiago” is etymologically related to “Didacus”, not for saying that “Diego” is etymologically related to “James”.
Now that I look at it again, maybe the problem is that the cite’s author mistyped “Therefore it cannot be said that Diego is either a Spanish or other linguistic form of James” when it was supposed to read “Therefore it cannot be said that Didacus is either a Spanish or other linguistic form of James.” That would certainly seem to make more sense in the context of the paragraph where it occurs, which is about the name Didacus and how Didacus isn’t etymologically related to Jacobos, not the name Diego.
Okay. I can see that conclusion: Didacus definitely does not equal Iacobus; Diego may derive from a misanalysis of Iacobus, from Didacus, or perhaps both. I’m looking around for an even more authoritative cite (in either direction), but with no luck.
Hanks & Hodges’ Oxford Dictionary of First Names agrees that Didacus > Diego, that Diego does not derive from Iago, but denies the Greek connection and claims it’s from some native Iberian language. I’m not sure if they mean Basque or a survival of an ancient language (Celtiberian? Lusitanian?). They’re normally a pretty good source but since there doesn’t seem to be a consensus among the various sources I’ll withdraw my emphatic “no way.”
Okay thanks Doc. I remain officially WTF’d on the topic of where the name “Diego” comes from.
I also remain puzzled as to why “Diego”, and apparently “Santiago” too, should be more popular counterparts of “James” in Spanish than the apparently just-as-good Iago.
And in case I didn’t have enough to be puzzled about, I find from Google that the place where the name “Iago” does still have quite a bit of popular recognition is…Wales. 
Okay, I give up.
Growing up, my family would watch Jesus Christ Superstar on Good Friday. When I got older and took an interest in Spanish, we watched it once with the Spanish subtitles. During the agony in the garden scene, Jesus asks why they couldn’t stay awake with him. He uses the name Santiago instead of James… and I didn’t get it for a while until I started learning Latin.