Dr. Dyson — math whiz turned physicist, humanist, author and cosmic visionary — was one of a kind, a polymath with a kaleidoscopic line of inquiry. Best known for his revolutionary calculations describing the interaction of light and matter, he produced valuable contributions to numerous fields, including solid state physics, ferromagnetism, astrophysics, biology and applied mathematics.

Often he sat along the eastern side of the institute’s dining room at a table for two, with a companion, or alone with his reading. Whenever I was there as a visitor, researching and writing, I sought him out. On one occasion in 2010, he suggested by email that we meet on the early side, at 12:15 p.m., “so as to be ahead of the mob of mathematicians.” He invariably arrived looking spiffy, in a tweedy sports jacket, shirt and tie. He usually got an entree, maybe roast beef with natural jus and braised carrots and mashed potato.

Over lunch on more than one occasion, I asked him about his 1983 paper “Unfashionable Pursuits.” Notoriously contrarian, he sought to identify unfashionable ideas that might later emerge as essential for 21st-century physics. “We ought to seek out and encourage the rare individualists who do not fit into the prevailing pattern,” he wrote. But he acknowledged that communal interest in fashionable problems served a purpose: The news and the rumors, “every petty success and every ephemeral triumph,” could be shared with friends at the lunch table.

Dr. Dyson was an anti-reductionist who liked to build bridges. His “Unfashionable Pursuits” paper surveyed the history of mathematics, and then, sixth-eighths of the way in, arrived at “the monster and the moral”: an entity that exists within the mathematical realm of symmetry, in the field of group theory. The “monster group” had been predicted to exist, and mathematicians hunted for verifying clues. Eventually, this creature was proved to live — or, technically, to act — in 196,883 dimensions, and to possess 808 sexdecillion or so symmetries. Dr. Dyson suggested that these symmetries might be connected to the symmetries of the universe. The monster and its ilk might seem like “a pleasant backwater in the history of mathematics,” he said. “But we should not be too sure that there is no connection.”