Diego Márquez Horrillo was a Spanish lawyer and politician. He was involved in several militant far-right movements, most notably as leader and founding member of the José Antonio Doctrinal Circles (Círculos Doctrinales José Antonio, CJA) and the political party Falange Española de las JONS. In his youth he was also a member of El Frente de Juventudes, an autonomous youth section of the Falange Española Tradicionalist and the Junats de Offensiva Nacional Sindicalista which was the only political party authorized by the Francois regime.

In 1977 the CJA participated in elections within the Alianza Nacional 18 de Julio coalition without success. In 1979 the Doctrinal Circles were integrated into FE de las JONS and Horrillo became leader, running for election within the Unión Nacional, a descendent of the Alianza Nacional 10 de Julio.

He died on March 27, 2014