The letter we know today as “A” has its roots in ancient Egyptian hieroglyphics where it was originally the pictogram of an ox head.
From Oxen to Alpha
The letter “A” we use today is descendant from the Greek letter Alpha. The first letter of the Greek alphabet, Alpha is actually the evolutionary result of other letter forms from other alphabets most notably the Phoenician letter / word Aleph meaning “ox.” Aleph looks like a sideways “A” pointing to the left which not-so-accidentally resembles a sideways ox head. But the history of the letter A goes back even further. The Phoenicians created Aleph as a simpler form of the even older Egyptian letter / sign of an ox head. The Egyptian pictogram for an ox is essentially an upside down “A”.
History of the Alphabet by Art of the Problem is a great video that explores the history and changes of language & writing from the more conceptual pictograms to the sound signs we use today. The invention of papyrus as a writing material gave the Egyptians a quicker way to record information than carving into stone. As papyrus became increasingly popular the Egyptians created what was essentially a hieroglyphics shorthand … hieroglyphics-lite if you will. This system eventually became the hieratic system of writing. It was a faster writing system designed to take advantage of this new writing technology they had created. Hieratic became easier to remember than hieroglyphics because it started to use less pictograms / word signs and instead used more sound signs, like our letters do today. With word signs you had to remember thousands of symbols to communicate. With sound signs you could combine symbols to create words. Hieratics eventually gave way to demotic, an even faster way for Egyptians to write. Over time the demotic sign for an ox became the basis for the Phoenecian aleph sign, which became alpha, which became our letter A.
So the letter A started as the image of an ox head in Egypt and as time past it worked its way around the Eastern coast of the Mediterranean up into Greece where it got turned upside-down into the letter Alpha and eventually our letter A.