Anders Olof Gunnar Källén (February 13, 1926 in Kristianstad, Sweden – October 13, 1968 in Hannover, Germany in a plane accident). Källén was a leading Swedish theoretical physicist and a professor at Lund University until his death at the age of 42.
Källén earned his doctorate at Lund in 1950 and worked from 1952 to 1957  at CERN's theoretical division in Copenhagen, which then became the Niels Bohr Institute. He also worked at Nordita 1957–1958 and then began a professorship at Lund University.
Källén's research focused on quantum field theory and elementary particle physics. His developments included the so-called Källén–Lehmann representation of correlation functions in quantum field theory, and he made contributions to quantum electrodynamics, especially in renormalizing. He also worked with the axiomatic formulation of quantum field theory, which led to contributions to the theory of functions of several complex variables. He collaborated on the Pauli–Källén equation. The function which appears in kinematical equations is called the Källén function.
Källén worked for several years at the Bohr Institute. Källén was flying his own plane from Malmö to CERN in Geneva when it crashed in 1968 . His two passengers, one of them his wife, survived the crash.
- G. Källén, Quantenelektrodynamik, Handbuch der Physik (Springer-Verlag, Berlin, 1958)
- G. Källén, Elementary Particle Physics (Addison-Wesley, Reading, Massachusetts, 1964)
- G. Källén, Quantum Electrodynamics (Springer-Verlag, Berlin, 1972)
- A. S. Wightman. Gunnar Källén 1926–1968, Comm. Math. Phys. 11 (1968) 181–182
- C. Jarlskog (Ed.) "Portrait of Gunnar Källén : A physics shooting star and poet of early quantum field theory" (Springer Verlag, ISBN 978-3-319-00627-7, 2014)