One of a Michelangelo themed set from 1961, this stamp features the head of the prophet Zechariah, as originally rendered on the Sistine Chapel Ceiling (see https://www.artbible.info/art/large/78.html).
Zechariah was a Hebrew prophet who wrote – handily – the Book of Zechariah. He was active around 520BC and is known as the 11th of the 12 Minor Prophets (I kind of want to dive into the merits of ranking systems on prophet performance, but I’ll leave it for now…). It’s also speculated that the book was written by not one but two people, so kick a prophet when he’s down, why don’t you?
Anyway, back to the Book. It tells broadly of the history of the Hebrews and the need for purity within the Temple, before flipping to some gently apocalyptic visions. It is often seen as source material for the Book of Revelation, which amped things up a bit. Zechariah wrote about four horsemen with different coloured horses and chariots as an image of the winds going out to north, south, east and west; later this morphed into the Four Horsemen of the Apocalypse. The second link below talks about the eight visions in Zechariah and gives some more explanation of their symbolism.