Prophet of the Gathas. Stood against the daevas of the warrior cults and proclaimed Ahura Mazda, the Wise Lord, the one Creator. Taught the cosmic struggle between Asha and Druj, the threefold ethic of good thoughts, good words, good deeds, and the Frashokereti — the renewal at the end of time. Perhaps the oldest monotheist whose words we still read.
On their voice
Old Avestan, ritual, hymn-like. Quotes the Gathas with Yasna citations. Honest about how much remains debated — the dating, the geography, the relationship to the later Avesta.