Euler, Pólya: By permission of Gerald Alexanderson. The portion of George Pólya’s letter in Chapter 17 is reproduced by permission of Andrew Odlyzko.
Peter the Great: The State Hermitage Museum, St. Petersburg. Artist: Jean Marc Nattier (1717).
Dirichlet, Gauss, Hilbert: Deutsches Museum.
Duke of Brunswick: Braunschweigisches Landesmuseum.
Riemann: The younger Riemann, by permission of Michael Monastyrsky; the older, courtesy of the Staatsbibliothek zu Berlin, Preussischer Kulturbesitz.
Dedekind, Landau, Siegel: Niedersächsische Staats- und Universitätsbibliothek, Göttingen; Abteilung für Handschriften und seltene Drucke.
de la Vallée Poussin: Louvain-la-Neuve, Archives de l’Université Catholique de Louvain, CHUL.
Hadamard: Archives of the Woodson Research Center, Fondren Library, Rice University.
Chebyshev: Scientific Library named after M. Gorky, St. Petersburg State University.
Connes, Montgomery, Odlyzko, Selberg: Copyright C.J. Mozzochi, Princeton, NJ.
Hardy, Littlewood: The Master and Fellows of Trinity College Cambridge.
Gram: The Royal Danish Academy of Sciences and Letters. (Detail from “A Meeting of the Academy,” by P.S. Krøyer, painted 1895-1897.)
Turing: The National Portrait Gallery, London.
Artin: Princeton University Library.
Weil, Deligne: Archives of the Institute for Advanced Study, Princeton. Photographers Herman Landshoff (Weil), Randall Hagadorn (Deligne).
Dyson: By permission of Freeman Dyson.
Berry: By permission of Sir Michael Berry.
Lindelöf: Helsinki University Museum. Artist: W. Sjörström (1930).
Cramér: By permission of Professor Anders Martin-Löf, Department of Mathematical Statistics, Stockholm University.
Taiye: By the author.