Yay! I love doing histories on letters of the alphabet!
For those new to my alphabet posts, let me give you some of its ancestry. The writing system we use in English is the Latin Alphabet, which was taken from the Etruscan alphabet somewhere before the sixth century BCE. The Etruscans were the people who lived in Italy prior to the rise of the Roman empire and little is known about them these days except by writings of other (rival) societies, but they did adapt an alphabet from the Euboean Greeks that passed on to the Romans, and thus, the rest of western Europe. The Greek alphabet is at least 2800 years old, a hell of a long time considering its still in use.
It was created using the Phoenician abjad—a consonant alphabet, meaning the Greeks added the vowels themselves. The Phoenicians developed their writing system over three thousand years ago, taking it from what we now call Proto-Sinaitic, which was created around 3900 years ago. Proto-Sinaitic was developed to aid the Canaanites that used it in their trades with other countries—keeping track of things was a lot easier when you were able to write down records. It’s also pretty much the ancestor of all of western civilization’s current alphabets, including Hebrew and Arabic along with our Latin. The symbols were taken from Egyptian heiroglyphs—they picked a word that began with the same sound, and used that glyph for it.
Now that that’s out of the way, I can get down to business. Look at this alphabet gif to get an idea of R’s evolution over the years. The early Latin R is missing it’s second leg, making it look an awful lot like P (P on the other hand is missing it’s closing loop, making it look like a backwards 1). It was backwards in Etruscan, but then frontwards (at least, from our point of view) back as the Greek rho. You can go here if you want a better look at rho’s history, where sometimes it actually looks like an R (so I guess it makes sense that we have it like that) and sometimes it even looks like a D!
In Phoenician, it’s resh, which means head, and it looks like a backwards P. Why would they do something like that? Well, resh, or rashu in proto-Sinaitic, means head. And what does that P symbol that means R kind of look like? A head. And that’s where R comes from.