When was Ballad of the Green Berets created?

The poem "Green Beret" by Ho Thien was translated and published (posthumously) sometime after 1966.

Robin Moore (1925-2008) wrote the novel "The Green Berets" in 1965 (ISBN 0-312-98492-8)

Barry Sadler (1940-1989) sang the hit song "Ballad of the Green Beret" in 1966.

The film "The Green Berets", starring actor John Wayne (1907-1979), was released in 1968.