Tarzan is the orphaned son of aristocratic English parents marooned in Africa in the late 1800's. Upon their deaths, he is adopted and raised by a band of apes which Burroughs calls "mangani", a species not otherwise known to science, but with characteristics of gorillas, chimpanzees, and early hominids, including a primitive form of speech. "Tarzan" is "White Skin" in the mangani language. His "real" English name is John Clayton III, Lord Greystoke.
His upbringing gives him physical skills considerably superior to those of the finest "civilized" athletes, but he also inherits a high level of mental prowess. He teaches himself to read by examining basic English primers left by his parents, and unlike the inarticulate barbarian version of him later popularized in films, eventually learns to speak several languages fluently.
Tarzan only makes contact with humans again when fully grown. At this stage, he learns to speak French and English and visits the civilised world, but then rejects this and returns to the jungle.
Later stories recount many further adventures, often featuring the discovery of lost civilizations.
Tarzan is a modern incarnation of the ancient literary tradition of "the hero raised by animals". Other examples are Mowgli from Rudyard Kipling's The Jungle Book, and the legendary founders of Rome, Romulus and Remus (raised by wolves).
The Tarzan story is informed by nonscientific ideas of evolution and "social darwinism" explored in much popular literature of this period, such as that of Jack London and Robert E. Howard. How much of our success or failure in life is due to our inheritance and how much to our own efforts? Are the conquests of some individuals and groups over others the result of a "natural" superiority, training, or sheer luck?