A, a a letter

a, letter that has stood at the head of the alphabet during the whole of the period through which it can be traced historically. The name of the letter in the Phoenician period resembled the Hebrew name aleph meaning “ox”; the form is thought to derive from an earlier symbol resembling the head of an ox. The letter was taken over by the Greeks in the form of alpha. In the Phoenician alphabet the letter stood for a species of breathing, as vowels were not represented in the Semitic alphabets.

https://www.britannica.com/topic/A-letter