Question: What Danish physicist did American theoretical physicist work with?
Context: Chris Quigg (born December 15, 1944) is an American theoretical physicist at the Fermi National Accelerator Laboratory (Fermilab).  He graduated from Yale University in 1966 and received his Ph.D. in 1970 under the tutelage of J. D. Jackson at the University of California, Berkeley.  He has been an associate professor at the Institute for Theoretical Physics, State University of New York, Stony Brook, and was head of the Theoretical Physics Department at Fermilab from 1977 to 1987. Benjamin Whisoh Lee (; January 1, 1935 – June 16, 1977) or Ben Lee, was a Korean-born American theoretical physicist.  His work in theoretical particle physics exerted great influence on the development of the standard model in the late 20th century, especially on the renormalization of the electro-weak model and gauge theory. Bill Sutherland (born March 31, 1942) is a notable American theoretical physicist.  He received his PhD in 1968 while studying under Nobel laureate C. N. Yang at Stony Brook.  He is best known for his work in statistical mechanics and quantum many body theory.  Early in his career he solved the six vertex model and developed an exact solution in 1967, which he then followed with the eight vertex model in 1970.  He completed his postdoctoral work at Berkeley in the 1969-1971 time frame where he became interested in inverse square potential many body interactions.  He then became a professor of physics at the University of Utah in 1971 where he worked until his retirement in 2004.  Most notably his name is associated with the Calogero-Sutherland model which is a major research area in theoretical physics and mathematics. Mary Katharine Gaillard (born April 1, 1939) is an American theoretical physicist with a focus on particle physics.  She is a professor of the Graduate School at the University of California, Berkeley and Visiting Scientist at the Lawrence Berkeley National Laboratory.  She was Berkeley's first tenured female physicist. David Jonathan Gross ( ; born February 19, 1941) is an American theoretical physicist and string theorist.  Along with Frank Wilczek and David Politzer, he was awarded the 2004 Nobel Prize in Physics for their discovery of asymptotic freedom.  David Gross is the Chancellor’s Chair Professor of Theoretical Physics at the Kavli Institute for Theoretical Physics of the University of California, Santa Barbara, and was formerly the KITP director and holder of their Frederick W. Gluck Chair in Theoretical Physics .  He is also a faculty member in the UC Santa Barbara Physics Department and is currently affiliated with the Institute for Quantum Studies at Chapman University in California.  He is a foreign member of the Chinese Academy of Sciences. Victor Frederick "Viki" Weisskopf (September 19, 1908 – April 22, 2002) was an Austrian-born American theoretical physicist.  He did postdoctoral work with Werner Heisenberg, Erwin Schrödinger, Wolfgang Pauli and Niels Bohr.  During World War II he was Group Leader of the Theoretical Division of the Manhattan Project at Los Alamos, and later campaigned against the proliferation of nuclear weapons. Mikhail "Misha" Voloshin (born 1953) is a Russian and American theoretical physicist.  Voloshin started working at ITEP in 1976 and accordingly earned his Ph.D. in 1977.  In 1983 he received a Soviet medal and an award in physics.  Since 1990 he started at the William I Fine Theoretical Physics Institute, University of Minnesota, a division of the University of Minnesota College of Science and Engineering where he teaches quantum physics.  In 1997 elected a fellow of the American Physical Society.  In 2001 he was awarded J.J. Sakurai Prize for Theoretical Particle Physics and in 2004 he was awarded the Alexander-von-Humboldt Award. John Archibald Wheeler (July 9, 1911 – April 13, 2008) was an American theoretical physicist.  He was largely responsible for reviving interest in general relativity in the United States after World War II.  Wheeler also worked with Niels Bohr in explaining the basic principles behind nuclear fission.  Together with Gregory Breit, Wheeler developed the concept of Breit–Wheeler process.  He is best known for linking the term "black hole" to objects with gravitational collapse already predicted early in the 20th century, for coining the terms "quantum foam", "neutron moderator", "wormhole" and "it from bit", and for hypothesizing the "one-electron universe". Niels Henrik David Bohr (] ; 7 October 1885 – 18 November 1962) was a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory, for which he received the Nobel Prize in Physics in 1922.  Bohr was also a philosopher and a promoter of scientific research. Burt Ovrut is an American theoretical physicist most famous for his work on heterotic string theory.  He is currently Professor of Theoretical High Energy Physics at the University of Pennsylvania.
Answer: Niels Bohr