The earliest known certain ancestor of "A" is aleph (also written 'aleph), the first letter of the Phoenician alphabet, which consisted entirely of consonants (for that reason, it is also called an abjad to distinguish it from a true alphabet).
ðɪ ˈɜːlɪɪst nˈoʊn sˈɜːʔn̩ ˈænsɛstɚɹ ʌv "ˈeɪ" ɪz ˈælɛf ˈɔːlsoʊ ɹˈɪʔn̩ ˈælɛf, ðə fˈɜːst lˈɛɾɚɹ ʌvðə foʊnˈɪʃən ˈælfəbˌɛt, wˌɪtʃ kənsˈɪstᵻd ɛntˈaɪɚli ʌv kˈɑːnsənənts fɔːɹ ðæt ɹˈiːzən, ɪɾ ɪz ˈɔːlsoʊ kˈɔːld ɐn ɐbdʒˈæd tə dɪstˈɪŋɡwɪʃ ɪt fɹʌm ɐ tɹˈuː ˈælfəbˌɛt.