Mandel was a theoretician of quantum optics (9 May (1927)–9 February 9 (2001)) and, with Emil Wolf, wrote an influential masterpiece book, as well as hosting the famous "Rochester Conferences". His most famous contribution is probably the Hong-Ou-Mandel effect (HOM) of two-photon interferences, which, however, might be more to the credit of Ou (this remains to be ascertained). Mandel made many early contributions to the statistics of light as well as to the problem of resonance fluorescence. It seems that, although being immensely famous in the field, this is still short of his actual contributions.