Jacques Hadamard

Jacques Hadamard was a great French Mathematician. He was a great-uncle of Laurent Schwartz, who reports numerous fantastic anecdotes about him in his biography. This one, of Hadamard looking for a job as a refugee from Nazi Europe, is my that is, Fabrice's. favourite:

He is famous in Quantum Information Processing for the Hadamard Gate $$\begin{equation} H= {1\over{\sqrt{2}}} \begin{pmatrix} 1 & 1\\ 1 & -1 \end{pmatrix}\,. \end{equation} $$ which is named after him as a particular case of his Hadamard matrices (matrices of $\pm1$ entries with perpendicular vectors).