[1] Acracio Martínez Prieto was born in Santurtzi as the son of an anarchist father, his named was changed to Horacio by the Bilbao civil registry of the Ollerías neighborhood.

An attack in Altos Hornos de Vizcaya meant for Horacio the beginning of a long series of dangerous incidents, which forced him into exile in France, leaving his mother, already a widow, in Bilbao.

In 1932 he was invited by the PCE to visit Russia along with the director of Tierra Vasca, but he returned with unfavorable impressions – he was initially cautious in sharing his views but later published a pamphlet that was critical of the Soviet system.

The outbreak of the Spanish Civil War surprised Prieto in Bilbao, where he represented the CNT in the Basque Defence Council until he moved to Barcelona.

Affiliated with the FAI, he was general director of commerce under the ministry of Juan López Sánchez (November 1936 – May 1937) and Undersecretary of Health under Segundo Blanco (April 1938 – February 1939).