Onésimo Díaz Hernández (born 16 August 1966) is a Spanish historian[1] known for his publications regarding the history of Spain in the twentieth century.

La primera expansion del Opus Dei durante los anos 1939 y 1940".

Díaz presented an article at the Conference of Association for Contemporary Iberian Studies, holds Association for Contemporary Iberian Studies, in Limerick at the University of Limerick, (Ireland, September 2004) on «Urquijo´s brother and the spanish modernization in the interwar period».

The study was cited in the book Francisco Morente Valero, "The Falange and the Academia: Falangist Intellectuals and the Idea of a National-Syndicalist University (1933-1943)".

[7][8] Díaz received the “Premio Leizaola" Award in 1994 for "En los orígenes de la autonomía vasca",[9] and in 1997 he received the “Premio Laudio-Llodio” Award for Los primeros Marqueses de Urquijo y Llodio.