Russian explorer of the southern Sudan and central Africa who determined the course of a major Congo River tributary, the Ubangi River, together with one of its branches, the Uele.

After journeys to Iceland (1869) and Tunis (1873–74), Junker went to Egypt and the Sudan (1875), where from 1876 to 1878 he explored the lower Sobat River and the western tributaries of the White Nile (White Nile River). In 1879 he went to Equatoria, the southernmost province of the Sudan, and spent part of the next several years with its governor, Mehmed Emin Paşa (Emin Pasha, Mehmed). Junker made ethnographic observations in the country of the Zande tribe, which now lies partly within the Central African Republic, Congo (Kinshasa), and The Sudan, and he established the identity of the Ubangi and Uele rivers. Prevented from returning to Europe through the Sudan because of the Mahdist uprising, Junker, carrying Emin's journals, crossed the heartland of what is now Tanzania and reached Zanzibar in December 1886. He wrote Reisen in Afrika, 1875–86 (1889–91; Travels in Africa).