The novel tells the story of John Clayton III. John and Alice (Rutherford) Clayton II, Lord and Lady Greystoke of England, are marooned in the western coastal jungles of equatorial Africa in 1888. In September 1889 their son John Clayton III is born. At one year old his mother dies, and soon thereafter his father is killed by the savage king ape Kerchak. The infant is then adopted by the she-ape Kala. Clayton is named "Tarzan" and raised in ignorance of his human heritage.
As a boy, feeling alienated from his peers due to their physical differences, he discovers his true parents' cabin, where he first learns of others like himself in their books. Using basic primers with pictures, over many years he teaches himself to read English, but having never heard it, cannot speak it. Upon his return from one visit to the cabin, he is attacked by a huge gorilla which he manages to kill with his father's knife, although he is terribly wounded in the struggle. As he grows up, Tarzan becomes a skilled hunter, exciting the jealousy of Kerchak, the ape leader, who finally attacks him. Tarzan kills Kerchak and takes his place as "king" of the apes. Later, a tribe of black Africans settle in the area, and Tarzan's adopted mother, Kala, is killed by one of its hunters. Avenging himself on the killer, Tarzan begins an antagonistic relationship with the tribe, raiding its village for weapons and practicing cruel pranks on them. They, in turn, regard him as an evil spirit and attempt to placate him.