German missionary and explorer, the first European to penetrate Africa from its Indian Ocean coast. Rebmann and his associate, Johann Ludwig Krapf, also were the discoverers of Kilimanjaro and Mt. Kenya and paved the way for the great East African explorations of the Britons Sir Richard Burton, John Hanning Speke, and David Livingstone.

Rebmann arrived in East Africa in 1846 and began missionary work among the coastal tribes. Though he felt he was only incidentally an explorer, he began expeditions into the interior and, in May 1848, was the first European to see Kilimanjaro. Krapf first sighted Mt. Kenya in December 1849. At first the existence of these mountains was not believed in Europe, but Rebmann's accounts, together with his sketch map of an enormous lake (Nyasa) in the interior, stimulated scientific exploration of the sources and drainage system of the Nile.