As envisioned by Burroughs, Opar is a lost colony of Atlantis located deep in the jungles of Africa, in which incredible riches have been stockpiled down through the ages.
After its initial appearance in Burroughs's second Tarzan novel, The Return of Tarzan (1913), Opar is revisited in the fifth, Tarzan and the Jewels of Opar (1916), the ninth, Tarzan and the Golden Lion (1923), and the fourteenth, Tarzan the Invincible (1930).