Make that two men named John, courtesy of today's Liturgy.
The first one "appeared in the desert, eating locusts and wild honey": John the Baptist. He also appears (by way of reference) in today's Gospel, where Jesus says John was the "greatest of all men born of woman." Greater than Abraham, who "believed and was justified"; greater than David, "a man after My own Heart." And yet a man who deliberately marginalized himself, withdrawing from the Levitical priesthood that was his by birth and even withdrawing from ordinary society, in order to better hear God's word and become "a voice in the desert, crying 'Prepare the way of the Lord!'"
The other John is the saint of the day, the humble Juan Diego. This John, too, lived in the desert. Juan Diego also deliberately marginalized himself, but in a different way than the Baptizer. Where the Baptizer had been born into a priestly family, Juan Diego was an unremarkable peasant among a conquered people. But he had marginalized himself even from his native people by becoming a Christian--one of the few early converts the Spanish missionaries managed to win.
But both men were "sent ahead" to prepare their people to receive the Lord. And in both men's lives, it was an encounter with Mary that made all the difference. Both of them, I think, could repeat the amazed words of the Baptizer's mother, Elizabeth: "Who am I, that the Mother of my Lord should come to me?"