Given the following context:

As a result of the Berlin Conference of 1884-1885, the Congo Basin is claimed by King Leopold II of the Belgians, who rules the Congo Free State in personal union with the Kingdom of Belgium. The country is on the verge of bankruptcy, Leopold having borrowed huge sums of money to finance the construction of railways and other infrastructure projects. He sends his envoy Léon Rom to secure the fabled diamonds of Opar. Rom's expedition is ambushed and massacred. A tribal leader, Chief Mbonga, offers Rom the diamonds in exchange for an old enemy: Tarzan.
The man once called "Tarzan", John Clayton III, has left Africa behind and settled down in London with his American-born wife, Jane Porter. He took up his birth name and ancestral family residence as Lord Greystoke. In the eight years since returning from Africa, John's story as Tarzan has become legendary among the Victorian public, although John wants to leave that past behind. Through the British Prime Minister, John is invited by King Leopold to visit Boma and report on the development of the Congo by Belgium; he declines to participate in the perceived publicity stunt.

answer the following question:

What is the nickname of the person who wants to leave their past behind? 

Tarzan