Short answers, pulled from the story.
Buchanan received the Nobel Memorial Prize in Economic Sciences in 1986 for his development of the contractual and constitutional bases for the theory of economic and political decision making. The Royal Swedish Academy of Sciences credited him with building what became known as public choice theory.
Public choice theory applies the methods of economics to political behavior, assuming that politicians, bureaucrats, and voters are primarily guided by self-interest rather than the public good. Buchanan called this framework "politics without romance." It first appeared systematically in The Calculus of Consent, co-authored with Gordon Tullock in 1962.
Buchanan co-authored The Calculus of Consent: Logical Foundations of Constitutional Democracy with Gordon Tullock, published in 1962. Tullock held a law degree rather than formal economics training, and Buchanan described them as complementary: Buchanan the philosopher, Tullock the scientist.
Buchanan held positions at the University of Tennessee, Florida State University, the University of Virginia, UCLA, and Virginia Tech before joining George Mason University in 1983, where he remained until retirement. He also established the Center for Study of Public Choice at Virginia Tech in 1969 and moved the entire unit to George Mason in 1983.
Frank Knight, a founding member of the Mont Pelerin Society and professor at the University of Chicago, taught Buchanan in 1945. Buchanan said that within six weeks of starting Knight's course he was "converted into a zealous advocate of the market order," having arrived describing himself as essentially socialist. Knight served as Buchanan's de facto PhD supervisor.
Democracy in Chains, a 2017 book by Duke University historian Nancy MacLean, argued that Buchanan worked alongside Charles Koch to limit democratic participation in ways that protected private wealth. Critics including Jean-Baptiste Fleury and Alain Marciano wrote in a 2018 Journal of Economic Literature review that MacLean had misunderstood public choice theory and overlooked significant aspects of Buchanan's biography. MacLean maintained that Buchanan's influence on modern conservatism was underappreciated.