Castro was born out of wedlock at his father's farm on 13 August 1926. His father, Ángel Castro y Argiz, a veteran of the Spanish–American War, was a migrant to Cuba from Galicia, Northwest Spain. He had become financially successful by growing sugar cane at Las Manacas farm in Birán, Oriente Province. After the collapse of his first marriage he took his household servant, Lina Ruz González – of Canarian origin – as his mistress and later second wife; together they had seven children, among them Fidel. At age six, Castro was sent to live with his teacher in Santiago de Cuba, before being baptized into the Roman Catholic Church at the age of eight. Being baptized enabled Castro to attend the La Salle boarding school in Santiago, where he regularly misbehaved; he was next sent to the privately funded, Jesuit-run Dolores School in Santiago. In 1945, Castro transferred to the more prestigious Jesuit-run El Colegio de Belén in Havana. Although Castro took an interest in history, geography and debating at Belén, he did not excel academically, instead devoting much of his time to playing sports.
In 1945, Castro began studying law at the University of Havana. Admitting he was "politically illiterate", Castro became embroiled in student activism and the violent gangsterismo culture within the university. Passionate about anti-imperialism and opposing U.S. intervention in the Caribbean, he unsuccessfully campaigned for the presidency of the Federation of University Students on a platform of "honesty, decency and justice". Castro became critical of the corruption and violence of President Ramón Grau's government, delivering a public speech on the subject in November 1946 that received coverage on the front page of several newspapers.
In 1947, Castro joined the Party of the Cuban People (Partido Ortodoxo), founded by veteran politician Eduardo Chibás. A charismatic figure, Chibás advocated social justice, honest government and political freedom, while his party exposed corruption and demanded reform. Though Chibás came third in the 1948 general election, Castro remained committed to working on his behalf. Student violence escalated after Grau employed gang leaders as police officers, and Castro soon received a death threat urging him to leave the university. However, he refused to do so and began to carry a gun and surround himself with armed friends. In later years, anti-Castro dissidents accused him of committing gang-related assassinations at the time, but these accusations remain unproven.
Rebellion and Marxism: 1947–1950
I joined the people; I grabbed a rifle in a police station that collapsed when it was rushed by a crowd. I witnessed the spectacle of a totally spontaneous revolution ... [T]hat experience led me to identify myself even more with the cause of the people. My still incipient Marxist ideas had nothing to do with our conduct – it was a spontaneous reaction on our part, as young people with Martí-an, anti-imperialist, anti-colonialist and pro-democratic ideas.
In June 1947, Castro learned of a planned expedition to overthrow the right-wing government of Rafael Trujillo, a U.S. ally, in the Dominican Republic. Being President of the University Committee for Democracy in the Dominican Republic, Castro joined the expedition. The military force consisted of around 1,200 troops, mostly Cubans and exiled Dominicans, and they intended to sail from Cuba in July 1947. Grau's government stopped the invasion under U.S. pressure, although Castro and many of his comrades evaded arrest. Returning to Havana, Castro took a leading role in student protests against the killing of a high school pupil by government bodyguards. The protests, accompanied by a crackdown on those considered communists, led to violent clashes between activists and police in February 1948, in which Castro was badly beaten. At this point, his public speeches took on a distinctly leftist slant by condemning social and economic inequality in Cuba. In contrast, his former public criticisms had centered on condemning corruption and U.S. imperialism.
In April 1948, Castro traveled to Bogotá, Colombia, leading a Cuban student group sponsored by President Juan Perón's Argentine government. There, the assassination of popular leftist leader Jorge Eliécer Gaitán Ayala led to widespread rioting and clashes between the governing Conservatives – backed by the army – and leftist Liberals. Castro joined the Liberal cause by stealing guns from a police station, but subsequent police investigations concluded that he had not been involved in any killings. Returning to Cuba, Castro became a prominent figure in protests against government attempts to raise bus fares. That year, he married Mirta Díaz Balart, a student from a wealthy family, through whom he was exposed to the lifestyle of the Cuban elite. The relationship was a love match, disapproved of by both families, but Díaz Balart's father gave them tens of thousands of dollars to spend on a three-month New York City honeymoon.
Marxism taught me what society was. I was like a blindfolded man in a forest, who doesn't even know where north or south is. If you don't eventually come to truly understand the history of the class struggle, or at least have a clear idea that society is divided between the rich and the poor, and that some people subjugate and exploit other people, you're lost in a forest, not knowing anything.
That same year, Grau decided not to stand for re-election, which was instead won by his Partido Auténtico's new candidate, Carlos Prío Socarrás. Prío faced widespread protests when members of the MSR, now allied to the police force, assassinated Justo Fuentes, a socialist friend of Castro's. In response, Prío agreed to quell the gangs, but found them too powerful to control. Castro had moved further to the left, influenced by the Marxist writings of Karl Marx, Friedrich Engels, and Vladimir Lenin. He came to interpret Cuba's problems as an integral part of capitalist society, or the "dictatorship of the bourgeoisie", rather than the failings of corrupt politicians, and adopted the Marxist view that meaningful political change could only be brought about by proletariat revolution. Visiting Havana's poorest neighborhoods, he became active in the student anti-racist campaign.
In September 1949, Mirta gave birth to a son, Fidelito, so the couple moved to a larger Havana flat. Castro continued to put himself at risk, staying active in the city's politics and joining the 30 September Movement, which contained within it both communists and members of the Partido Ortodoxo. The group's purpose was to oppose the influence of the violent gangs within the university; despite his promises, Prío had failed to control the situation, instead offering many of their senior members jobs in government ministries. Castro volunteered to deliver a speech for the Movement on 13 November, exposing the government's secret deals with the gangs and identifying key members. Attracting the attention of the national press, the speech angered the gangs and Castro fled into hiding, first in the countryside and then in the U.S. Returning to Havana several weeks later, Castro lay low and focused on his university studies, graduating as a Doctor of Law in September 1950.
Castro co-founded a legal partnership that primarily catered to poor Cubans, although it proved a financial failure. Caring little for money or material goods, Castro failed to pay his bills; his furniture was repossessed and electricity cut off, distressing his wife. He took part in a high school protest in Cienfuegos in November 1950, fighting with police to protest the Education Ministry's ban on student associations; he was arrested and charged for violent conduct, but the magistrate dismissed the charges. His hopes for Cuba still centered on Chibás and the Partido Ortodoxo, and he was present at Chibás' politically motivated suicide in 1951. Seeing himself as Chibás' heir, Castro wanted to run for Congress in the June 1952 elections, though senior Ortodoxo members feared his radical reputation and refused to nominate him. He was instead nominated as a candidate for the House of Representatives by party members in Havana's poorest districts, and began campaigning. The Ortodoxo had considerable support and was predicted to do well in the election.
During his campaign, Castro met with General Fulgencio Batista, the former president who had returned to politics with the Unitary Action Party. Batista offered him a place in his administration if he was successful; although both opposed Prío's administration, their meeting never got beyond polite generalities. On 10 March 1952, Batista seized power in a military coup, with Prío fleeing to Mexico. Declaring himself president, Batista cancelled the planned presidential elections, describing his new system as "disciplined democracy"; Castro was deprived of being elected in his run for office by Batista's move, and like many others, considered it a one-man dictatorship. Batista moved to the right, solidifying ties with both the wealthy elite and the United States, severing diplomatic relations with the Soviet Union, suppressing trade unions and persecuting Cuban socialist groups. Intent on opposing Batista, Castro brought several legal cases against the government, but these came to nothing, and Castro began thinking of alternate ways to oust the regime.