Lewis & Short

alpha, n. indecl., = ἄλφα, the Greek name of the first letter of the alphabet: hoc discunt ante alpha et beta, before their letters, before they learn to read, Juv. 14, 209.
Hence, prov., the first in any thing (as beta was the second): alpha paenulatorumbeta togatorum, Mart. 5, 26; so by character instead of name: Ego sum Α et Ω, principium et finis, Vulg. Apoc. 1, 8; 21, 6; 22, 13.