The phantom (1943)

Two expeditions are trying to reach the Lost City of Zoloz -- one headed by Professor Davidson, a scientist who wants to establish an archaeological site, and the other by a greedy treasure hunter who wants to keep the fabled treasures of the city for himself. An agent of a foreign power also wants to establish a secret airbase there, so he stirs up the natives against The Phantom, who has been able to get them to stay peaceful so far. When The Phantom is murdered, his son takes his place and sets out to restore peace to the jungle and stop the agents' and the treasure hunters' nefarious plans.