Baldomero Espartero (1793 - 1879) was a Spanish general and political figure. He was associated with the radical (or progressive) wing of Spanish liberalism and would become their symbol and champion after taking credit for the victory over the Carlists in 1839. It was against this backdrop that Espartero's political opponents, the moderates, mobilised support to amend the progressive Constitution of 1837. In particular, the moderates' proposal to abolish democratically-elected local councils threatened to destroy the powerbase of the progressives. This threat was checked by the radical revolution of 1840, after which the conservatives were sidelined and Espartero became the master of the destiny of Spain. Forcing the Regent, Maria Cristina , into exile for her conspiracy with the moderates, Baldomero Espartero himself became Regent with the intention of remaining so until the future Queen Isabel came of age. Espartero's popular support enabled him to crush moderate military uprisings across Spain in 1841. Yet his ruthless execution of dozens of the conspirators, including many popular fellow war heroes like Diego de Leon , as well as his hasty and ungrateful dissolution of the radical juntas that had crushed the risings, marked the start of the decline in support for his regency. Economic slump and rumours of a free-trade deal with Britain provoked a popular uprising by workers and the bourgeoisie of Barcelona in 1842. Espartero's ruthless bombardment of the city crushed this revolutionary threat. But a second uprising in 1843 combined with moderate conspiracies and military uprisings which obliged the Regent to leave Spain for Britain.

Dubbed public enemy number one by the brutal forces of reaction headed by the moderate General Narvaez, Espartero was unable to return to his estates in Northern Spain until an amnesty decreed later in the 1840s. Although Espartero's regime 1840-1843 in reality had done little for Spain's poor, the anti-radical reaction of the moderates made the former Regent a folk-hero amongst many of the workers. Therefore, it was logical that he should become head of the short-lived "Progressive Biennium " of 1854-1856. But, as Karl Marx observed, the progressive caudillo was a man whose time had passed. When Spanish political power swung once more back towards the moderates in 1856, Espartero retired into the role of senator and elder statesman, finally ending his long life on his estate in La Rioja in 1879.