Rev. Johann Georg Reuther (1861-1914) was a German-speaking Lutheran missionary who was in charge of Bethesda mission at Lake Killalpaninna (near Cooper Creek, east of Lake Eyre, South Australia) from 1888 to 1906. In addition to his missionary work and running the farm and pastoral property, Reuther carried out anthropological research on Diyari (which he called Diari) language and culture. Between 1892 and 1894 Reuther and Rev. Carl Strehlow translated the New Testament into Diyari; it was published as Testamenta Marra in 1897. You can find out more information about Reuther here and here and in Stevens 1994 (in References).
Here is a picture of Reuther and his wife Pauline taken in his study at Killalpaninna.
Reuther left the mission in 1906 and moved to Eudunda (near Point Pass) in South Australia. He died by drowning in a horse and cart accident in 1914. His manuscripts and ethnographic collection were purchased by the South Australian Museum in 1917.