Politician, writer and professor of history at the University of Madrid. He participated in the Revolution of 1868 and was the fourth president of the First Spanish Republic. He was also a member of the Royal Spanish Academy.

Castelar was very critical of Queen Isabell II’s politics. He criticized the fact that the Queen gave her patrimony to the Spanish Nation in 1865. He called it a maneuver because the monarchy was in debt. Castelar when into exile to France in 1866 and returned to Spain when Isabell II was expeled, after the 1868 Gloriosa Revolution. 

Emilio Castelar drafted the Constitution of 1869. A copy of the manuscript is currently held at the Biblioteca Nacional de España in Madrid.

Castelar believed in universal suffrage, the right of association, the freedom of worship and the establishment of trials with popular jury.