Question: Joseph Wolf became the preferred illustrator for this explorer who  had an obsession with discovering the sources of the Nile River 
Sentence (from "David Livingstone"): His fame as an explorer and his obsession with discovering the sources of the Nile River was founded on the belief that if he could solve that age-old mystery, his fame would give him the influence to end the East African Arab-Swahili slave trade.
Relevant evidence: Yes