German gardener, colonial servant, plantation owner. Born in Leipzig, the son of orientalist Theodor Zenker and Baroness Rehbinder of Astrachan, he had little interest in school and left to become a gardener and apprentice at the Botanical Gardens from 1875-1878, until called for military service. Afterwards he went to Italy, where he worked as a head gardener at the botanical gardens in Naples. He married there, only to have his young wife die a year later. Then, in 1886, he set out for the Congo on a fact-finding trip for the Italian government, eventually moving on to Gabon where he was put in charge of the Sibange Farm near Libreville, well known for the collections of Soyaux and B⟼ttner. From there he went to Cameroon, then a German possession, to collect and cultivate native plants and became the "Preparator for geological, zoological and botanical purposes" on the Yaounde Station. Cut off for three years from any outside contact because of hostilities between tribes of the Botanga coast and those of the hinterland, he was awarded a medal for remaining at his post under difficult circumstances. He committed himself to three more years in the German colonial service.

As the only European on the Yaounde Station, Zenker's isolation brought about a decisive change in his life. He was regarded by the colonial service as having 'gone native', living and working alongside the African workers at the station. A Tongolese woman took charge of his household and remained his companion into his old age; a Cameroonian woman taught him the local language and customs, and the meaning of the drum messages used to communicate between villages. From these women he had three sons, whom he recognised as his lawful family and sent to Germany for their education. In 1895 he left the colonial service and returned to Germany, after almost ten years abroad, only to emigrate privately to Cameroon and set up the plantation Bipindihof (Bipinde), where he grew cocoa, coffee and rubber. In 1922 he fell ill with kidney trouble and died.

Zenker was a passionate collector. After a visit in 1897, Governor von Puttkamer wrote: "His house was a complete museum full of ethnographic curiosities, photographs, oil and watercolour paintings, herbaria, furs and skulls, weapons, fetishes, stuff birds, etc." His outhouses were stacked with boxes of plants and zoological objects, including the cadaver of a giant stork. When his first Cameroonian collections reached Berlin in 1893, the many coloured sketches and specimens of remarkable new plants such as Pterorhachis Harms and Schumanniophyton Harms (= Tetrastigma K. Schum) excited great enthusiasm. Through his collections and discovery of West African flora, Zenker earned wide recognition; many African plant species were named after him, including Agelaea zenkeri G. Schellenb., Anthericum zenkeri Engl. and Diplazium zenkeri Hieron. He is also commemorated in the names of a number of mammals and birds. Sadly, the original plant material sent to Berlin was mostly destroyed (1943) during the Second World War.