He finds his way to a rocky place known as Dark Cliff after he was chased by Sabor the leopard, inhabited by two hulking, spoiled gorilla brothers, the dim-witted Uto, the exceedingly violent Kago, and their controlling, over-protective Mama Gunda. But they fear the Zugor as much as Tarzan does, and when the booming call of the monster echoes through the valley, Tarzan is able to escape from them.
He encounters a bad-tempered, old gorilla who at first keeps the boy distant, but Tarzan discovers that this old gorilla actually is Zugor, who uses hollow trees as megaphones to amplify his voice and pretend to be a monster to scare other jungle creatures away from his territory and food. Tarzan uses this discovery to force Zugor into letting the boy stay with him. Thanks to Tarzan's cheerfulness and helpfulness, Zugor begins to warm to him as the boy continues to try to figure out what he is.