Theodor Koch-Grünberg (9 April 1872, Grünberg, Hesse, German Empire – 8 October 1924, Caracaraí, Brazil) was a German ethnologist and explorer who made a valuable contribution to the study of the Indigenous peoples in South America, in particular the Pemon Indians of Venezuela and the indigenous population of Brazil in the Amazon region. The 2015 film El abrazo de la serpiente (Embrace of the Serpent) fictionalizes his illness and final days based on his journals. He was played by actor Jan Bijvoet.
After studying humanities at the University of Tübingen, he obtained a doctorate in philosophy at Würzburg with a thesis on the Guaicuru.
In 1896 he travelled to Brazil for the first time as a member of an expedition led by Hermann Meyer in search of the source of the Xingu River, a tributary of the Amazon River.
Then from 1903–1905 he explored the Yapura River and the Rio Negro to the border with Venezuela. In 1906, he published photogravures of people he encountered on the expedition in his monumental "Indianertypen aus dem Amazonasgebiet nach eigenen Aufnahmen während seiner Reise in Brasilien" (1906).
A written account of his trip, including his study of the Baniwa, was published in two volumes in 1910-11 under the title: Zwei Jahre Unter Den Indianern. Reisen in Nord West Brasilien, 1903-1905 (Two Years Among the Indians. Travels in North-West Brazil).