Gell-Mann, along with Maurice Lévy, developed the sigma model of pions, which describes low-energy pion interactions. In 1964, Gell-Mann and, independently, George Zweig went on to postulate the existence of quarks, particles of which the hadrons of this scheme are composed. The name was coined by Gell-Mann and is a reference to the novel "Finnegans Wake", by James Joyce ("Three quarks for Muster Mark!" book 2, episode 4). Zweig had referred to the particles as "aces", but Gell-Mann's name caught on. Quarks, antiquarks, and gluons were soon established as the underlying elementary objects in the study of the structure of hadrons. He was awarded a Nobel Prize in Physics in 1969 for his contributions and discoveries concerning the classification of elementary particles and their interactions. In the 1960s, he introduced current algebra as a method of systematically exploiting symmetries to extract predictions from quark models, in the absence of reliable dynamical theory. This method led to model-independent sum rules confirmed by experiment and provided starting points underpinning the development of the Standard Model (SM), the widely accepted theory of elementary particles. In 1972 he and Harald Fritzsch introduced the conserved quantum number "color charge", and later, together with Heinrich Leutwyler, they coined the term quantum chromodynamics (QCD) as the gauge theory of the strong interaction. The quark model is a part of QCD, and it has been robust enough to accommodate in a natural fashion the discovery of new "flavors" of quarks, which superseded the eightfold way scheme. Gell-Mann was responsible, together with Pierre Ramond and Richard Slansky, and independently of Peter Minkowski, Rabindra Mohapatra, Goran Senjanović, Sheldon Lee Glashow, and Tsutomu Yanagida, for the seesaw theory of neutrino masses, that produces masses at the large scale in any theory with a right-handed neutrino. He is also known to have played a role in keeping string theory alive through the 1970s and early 1980s, supporting that line of research at a time when it was a topic of niche interest. At the time of his death, Gell-Mann was the Robert Andrews Millikan Professor of Theoretical Physics Emeritus at California Institute of Technology as well as a University Professor in the Physics and Astronomy Department of the University of New Mexico in Albuquerque, New Mexico, and the Presidential Professor of Physics and Medicine at the University of Southern California.