Jakob Johann Baron von Uexküll (German: [ˈʏkskʏl]; 8 September 1864 – 25 July 1944) was a Baltic German biologist who worked in the fields of muscular physiology, animal behaviour studies, and the cybernetics of life. However, his most notable contribution is the notion of Umwelt, used by semiotician Thomas Sebeok and philosopher Martin Heidegger. His works established biosemiotics as a field of research.