As a member of the avant-garde in mathematics in France in the 1930s he made his name as a founder of the Bourbakigroup, which owed its moniker to a prank theorem named after a general in Napoleon III's army.
Formal proof is a notion developed in the early part of the 20th century by logicians such as Bertrand Russell and Gottlob Frege, along with mathematicians such as David Hilbert (who can fairly be described as the father of modern mathematics) and Nicolas Bourbaki, the pseudonym of a group of French mathematicians who sought to place all of mathematics on a rigorous footing.