I'm sure Spiros/Spyros/Speros won't mind if I explain...
The Greek name Σπύρος is a short form of Spyridon - as in the patron saint of the island. The third Greek letter is upsilon, which is maybe halfway between the u in "put" (southern English pronunciation) and "ee" like in the vowel in "peach." English does not have an exact equivalent of upsilon, so the normal transcription to English characters is either i or y - Spiros or Spyros.
Spiros (and cousin Dmitris - Little Prince) were educated in America. Americans are utterly incapable of pronouncing any foreign language correctly. They will almost always pronounce a "foreign" i as "eye" - for example the ancient city of Delphi, which should be pronounced THE-ell-phee they will say as Delph-EYE.
Spiros told me he was fed up with having his name pronounced SPIE-ross, so he at first altered it to Speeros for popular consumption, and then thought that was inelegant, so contracted it to Speros. Like so many things in life, these accidents of history remain, and depending on the weather, the phase of the moon and so on he will either write it as Spiros or Speros. Ultimately, it is Σπύρος.
Asking Σπύρος about his name is a good excuse to go and have some fabulous food at Nafsika. I'm already looking forward to it!