Hannes Olof Gösta Alfvén (30 May 1908; Norrköping, Sweden – 2 April 1995; Djursholm, Sweden) was a Swedish plasma physicist and Nobel laureate for his work on the theory of magnetohydrodynamics. He was originally trained as an electrical power engineer and later moved to research and teaching in the fields of plasma physics. Alfvén made many contributions to plasma physics, including theories describing the behavior of aurorae, the Van Allen radiation belts, the effect of magnetic storms on the Earth's magnetic field, the terrestrial magnetosphere, and the dynamics of plasmas in the Milky Way galaxy.