Friedrich-Karl "Friedel“ Thielemann (born 17 April 1951 in Mülheim an der Ruhr) is a German-Swiss theoretical astrophysicist.
In 1980 he earned his PhD under Wolfgang Hillebrandt (in Garching) and E. R. Hilf in nuclear astrophysics.
As a post-doc he was with David Schramm and William David Arnett at the University of Chicago, William A. Fowler at Caltech, Hans Klapdor at the Max-Planck-Institut für Kernphysik, am Max-Planck-Institut für Astrophysik in Garching (with Hillebrandt) and at the University of Illinois (with James W. Truran).
He investigated, among other things, supernovae, X-ray bursts, gamma ray bursts, fusion of neutron stars, emergence of heavy elements, and evolution of chemical elements in galaxies.
In 1998 he was elected a fellow of the American Physical Society for "his work at the interface of nuclear physics and astrophysics and the applications to stellar nucleosynthesis, Type Ia and Type II Supernovae, as well as the r- and rp-process.