Have you ever seen a place that calls itself ye olde whatever?" As it happens,
that's not a "y," or, at least, it wasn't supposed to be. Originally, it was an
entirely different letter called thorn, which derived from the Old English
runic alphabet, Futhark.
Thorn, which was pronounced exactly like the "th" in its name, is actually
still around today in Icelandic. We replaced it with "th" over time - thorn fell
out of use because Gothic-style scripting made the letters y and thorn look
practically identical. Typographically, the lower case thorn character is
unusual in that it has both an ascender and a descender.
Another holdover from the Futhark runic alphabet, wynn was adapted to the Latin
alphabet because it didn't have a letter that quite fit the "w" sound that was
common in English. You could stick two u's (technically v's, since Latin didn't
have u either) together, like in equus, but that wasn't exactly right.
Over time, though, the idea of sticking two u's together actually became quite
popular, enough so that they literally became stuck together and became the
letter W (which, you'll notice, is actually two V's).