Leo Yaffe was born in Devil's Lake, North Dakota. He earned a B.Sc. in chemistry from the University of Manitoba in 1940, an M.Sc. in 1941 and a doctorate in radiochemistry from McGill in 1943. From 1943 until 1952, he worked for Atomic Energy of Canada Ltd. as a project leader in nuclear chemistry and tracer research. Yaffe returned to McGill as a Lecturer in 1954, was promoted to Associate Professor in 1954, and was named Macdonald Professor of Chemistry in 1958. From 1963 to 1968 he directed research at the International Atomic Energy Agency in Vienna. He served as Chairman of the Chemistry Department form 1965 to 1972, and as Vice-Principal (Administration) from 1974 to 1981.

The XY Company was formed in an agreement dated 20 October 1798 by the union of Forsyth, Richardson and Co. with Leith Jamieson and Co. Its foundation arose from conflicts between North West Company agents (namely, Simon McTavish) and North West Company winterers. The firm of Parker, Gerrard, Ogilvy and Company was the principal shareholder. The company's first outfit was from fall to spring 1799. As the XY Company entered into the North West, going as far as Athabasca, they entered into direct competition with the North West Company. The company was dissolved in November 1804, shortly after McTavish's death in July, and merged with the North West Company.