Gabriel Andrew Dirac (13 March 1925 – 20 July 1984) was a Hungarian-British mathematician who mainly worked in graph theory.^[1] He served as Erasmus Smith's Professor of Mathematics at Trinity College Dublin from 1964 to 1966.^[2] In 1952, he gave a sufficient condition for a graph to contain a Hamiltonian circuit. The previous year, he conjectured that n points in the plane, not all collinear, must span at least ${\displaystyle \lfloor n/2\rfloor }$ two-point lines, where ${\displaystyle \lfloor x\rfloor }$ is the largest integer not exceeding ${\displaystyle x}$. This conjecture was proven true when n is sufficiently large by Green and Tao in 2012.^[3]

Dirac started his studies at St John's College, Cambridge in 1942, but in that same year, the war saw him serving in the aircraft industry.^[1] He received his MA in 1949, and moved to the University of London, getting his Ph.D. "On the Colouring of Graphs: Combinatorial topology of Linear Complexes" there under Richard Rado.^[4]

Dirac's main academic positions were at the King's College London (1948-1954), University of Toronto (1952-1953), University of Vienna (1954-1958), University of Hamburg (1958-1963), Trinity College Dublin (Erasmus Smith's Professor of Mathematics, 1964-1966), University of Wales at Swansea (1967-1970), and Aarhus University (1970-1984).^[1]

He was born Balázs Gábor in Budapest, to Richárd Balázs, a military officer and businessman, and Margit "Manci" Wigner (sister of Eugene Wigner).^[5] When his mother married Paul Dirac in 1937, he and his sister resettled in England and were formally adopted, changing their family name to Dirac.^[6] He married Rosemari Dirac and they had four children together: Meike, Barbara, Holger and Annette.^[7]

• Dirac's theorem on Hamiltonian cycles
• Dirac's theorem on chordal graphs
• Dirac's theorem on cycles in k-connected graphs

• L. Døvling Andersen, I. Tafteberg Jakobsen, C. Thomassen, B. Toft, and P. Vestergaard (eds.), Graph Theory in Memory of G.A. Dirac, Annals of Discrete Mathematics, volume 41, North-Holland, 1989. ISBN 0-444-87129-2.