Yay! I love letter origins! And of course, I want to know the truth about J, the letter that starts my own name. So let’s look at the alphabet gifand…
Hm. That’s it? It came from I/iota? Well, yes. Back in the days when Latin wasn’t a dead language and Jupiter was Iuppiter, it didn’t exist.
J first started as nothing more than an I with an extra-long hook on the bottom. Medieval Writing has a great page on the formation of J in Gothic writing. It started as a way to distinguish the double I’s in words. Then the Dutch started using J as a long I sound. This is the reason that many languages have J as a soft sound. In Spanish it’s “huh” as in Julio or Jueves. Or you can think of the “yuh” sound, like in fjord, a word of Norwegian extract.
It was the Italian writer Gian Giorgio Trissino who first used the letter with the “juh” sound way back in 1524. As to why he needed another letter when G was there, I have no idea, but it caught on, although the Romance languages are the only one who really keep it that way.
TL;DR: Started as an I clone, turned into a soft G clone. At least in English.
The Alphabet Gif