Question: Joseph Wolf became the preferred illustrator for this explorer who  had an obsession with discovering the sources of the Nile River 

Context paragraphs:
Greater Upper Nile: The Greater Upper Nile is a region of northeastern South Sudan.  It is named for the White Nile, a tributary of the Nile River in North and East Africa.

Fashoda Incident: The Fashoda Incident or Crisis was the climax of imperial territorial disputes between Britain and France in Eastern Africa, occurring in 1898.  A French expedition to Fashoda on the White Nile river sought to gain control of the Upper Nile river basin and thereby exclude Britain from the Sudan.  The French party and a British-Egyptian force (outnumbering the French by 10 to 1) met on friendly terms, but back in Europe, it became a war scare.  The British held firm as both empires stood on the verge of war with heated rhetoric on both sides.  Under heavy pressure the French withdrew, securing Anglo-Egyptian control over the area.  The status quo was recognised by an agreement between the two states acknowledging British control over Egypt, while France became the dominant power in Morocco.  France had failed in its main goals.  P.M.H. Bell says:

Burkhart Waldecker: Burkhart Waldecker was a German explorer who, in 1937, discovered the most southern source of the White Nile in Burundi.  Waldecker came to the area to seek asylum from Nazi persecution.  The true source is near Rutovu, where a pyramid was erected in 1938.  Waldecker's name is seen on the plaque, which says in Latin, "Caput Nili," thus ending man's long quest to discover the source.  The Nile river has various sources, Waldecker found the White Nile's most southern source which is part of the Kagera River, the other being Lake Kyoga in Uganda further north.  The small pipe flowing with the first Nile water appears from the ground below the summit of Mount Kikizi where the pyramid is found.

Nile, Texas: Nile is an abandoned ghost town in Milam County, Texas, nine miles west of Rockdale, and is named after the river in Egypt, the Nile River.  The population peaked at thirty-five in 1896 when it had two cotton gins, and a general store.  The school, which had forty-three students in 1903, consolidated with Thorndale in 1946.  Today, nothing, not even a modest cemetery, remains in Nile.

Hymn to the Nile: Occurring at about 450 BCE, Herodotus—a Greek historian—called Egypt the “Gift of the Nile” because ancient Egyptian civilization depended on the resources from the river so they could continue living in that vicinity.  Beyond the Nile River is the Sahara Desert, and since it almost impossible to grow food in the desert, very few people lived far from the river itself.  People that were settled close to the banks of the Nile shared the same language and also worshipped similar gods.  "Hymn to The Nile" is a tune that was created and sang by the ancient Egyptian peoples about the flooding of the Nile River and all of the miracles it brought to Ancient Egyptian civilization.  Because the ancient Egyptians had relied on this miracle river, Egypt was the “Gift of the Nile.”

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.  "The Nile sources," he told a friend, "are valuable only as a means of opening my mouth with power among men.  It is this power which I hope to remedy an immense evil."  His subsequent exploration of the central African watershed was the culmination of the classic period of European geographical discovery and colonial penetration of Africa.  At the same time, his missionary travels, "disappearance", and eventual death in Africaand subsequent glorification as a posthumous national hero in 1874led to the founding of several major central African Christian missionary initiatives carried forward in the era of the European "Scramble for Africa".

Nile boat: The Nile River is a major resource for the people living along it, especially thousands of years ago.  The El Salha Archaeological Project discovered an abundance of evidence of an ancient boat that traveled the Nile River dating back to 3,000 years ago.  Pictographs and pebble carvings were uncovered, indicating a boat more advanced than a simple canoe.  This evidence of a progressed Nile boat includes a steering system which may have been used in the Nile for fishing and transportation.

Joseph Wolf: Joseph Wolf (21 January 1820 – 20 April 1899) was a German artist who specialized in natural history illustration.  He moved to the British Museum in 1848 and became the preferred illustrator for explorers and naturalists including David Livingstone, Alfred Russel Wallace and Henry Walter Bates.  Wolf depicted animals accurately in lifelike postures and is considered one of the great pioneers of wildlife art.  Sir Edwin Landseer thought him "...without exception, the best all-round animal artist who ever lived"'.

Nile Expedition: The Nile Expedition, sometimes called the Gordon Relief Expedition (1884–85), was a British mission to relieve Major-General Charles George Gordon at Khartoum, Sudan.  Gordon had been sent to the Sudan to help Egyptians evacuate from Sudan after Britain decided to abandon the country in the face of a rebellion led by self-proclaimed Mahdi, Mahommed Ahmed.  A contingent of Canadians was recruited to help the British navigate their small boats up the Nile River.  The Nile Expedition was the first overseas expedition by Canadians in a British imperial conflict, although the Nile Voyageurs were civilians employees and did not wear uniforms.

Panayotis Potagos: Panayotis Potagos (1839-1903) was a Greek physician and explorer from Arcadian Vytina.  Potagos began his travels in 1867, visiting Iraq, Iran, Afghanistan, Gobi Desert, and India.  He arrived in Egypt in 1876, ascending the Nile River to southern Sudan and then crossed the Congo-Nile Divide into the Congo River basin through what is now the Central African Republic and finally reached the Uele River in 1877.  He was the first to reach Mbomu and Uele rivers from the north.  He published an account of his travels, which was translated in French.

Supporting paragraphs: Joseph Wolf David Livingstone
Answer: David Livingstone