Indalecio Prieto Tuero (April 30, 1883 – February 11, 1962) was a Spanish politician, one of the leading figures of the Spanish Socialist Workers' Party (PSOE) in the years before and during the Second Spanish Republic.

Born in Oviedo in 1883, his father died when he was six years old; his mother moved him to Bilbao in 1891. From a young age, he survived by selling magazines in the street; he eventually obtained work as a stenographer at the daily newspaper La Voz de Vizcaya. This led to a position as a copy editor and later a journalist at rival daily El Liberal; his career there eventually made him the director and proprietor.^{[citation needed]}

In 1899 he joined the PSOE. As a journalist in the first decade of the 20th century, Prieto became a leading figure of socialism in the Basque Country.

Spain's neutrality in World War I greatly benefited Spanish industry and commerce, but those benefits were not reflected in the workers' salaries. This led to a great deal of social unrest, culminating on August 13, 1917 in a revolutionary general strike. Fear of a repetition of the then-recent February Revolution in Russia (the October Revolution was still to come), the general strike was harshly put down by the military, and the members of the strike committee were arrested in Madrid. Having been involved in the organization of the strike, Prieto fled to France before he could be arrested; he did not return until April 1918, by which time he had been elected to the Spanish Congress of Deputies.