Raúl Castro has announced his resignation as head of the Cuban Communist Party, putting an end to his family's six decades in power.
Castro, 89, told a party congress that he is passing the baton to a younger generation "full of passion and anti-imperialist spirit".
At the end of the four-day congress, his successor will be elected, reports BBC.
The step, which was planned, brings an end to his and his brother Fidel Castro's period of structured leadership, which started with the 1959 revolution.
He told party delegates in Havana on Friday, "I believe fervently in the strength and exemplary nature and comprehension of my compatriots,"
Although Castro has not endorsed a successor, it is generally assumed the party leadership will pass to Miguel Díaz-Canel, the island's president since 2018.
End of an era
For the first time in more than six decades, Cuba's politics will be led by anyone other than Castro.
Since 2011, Raúl has served as the party's secretary-general, succeeding his older brother, Fidel.
Raúl was one of Fidel Castro's commanders during the socialist revolution that overthrew the Cuban government in 1959.
Fidel Castro was the country's leader until 2006, when he became ill and turned over the presidency to his brother, Raúl. In 2016, Fidel Castro passed away.
Cuba under Raúl
Raúl Castro kept the communists' one-party rule intact.
Between 2014 and 2016, he witnessed an expansion in ties with the United States, including landmark talks with President Barack Obama in 2016.
However, under Donald Trump's administration, tensions rose as sanctions were tightened.
While the White House said on Friday that a change in Cuban policy was not one of Biden's highest priorities, he has promised to ease some of Trump's sanctions.
Raúl Castro said at the congress on Friday that his country was willing to "develop respectful dialogue" with the US but would not consider "concessions" on its "foreign policy and ideals."
The transition at the head of Cuba's ruling party comes as the country grapples with its worst economic recession in decades.
The Covid-19 pandemic, as well as the Trump administration's financial reforms and sanctions, have taken a toll on the economy, which shrank by 11% last year.
The long-awaited currency reform, which took effect on January 1, aimed to improve the efficiency of the economy and state-owned enterprises. However, it has severely strained the finances of average Cubans.
Many people have advocated for the country to have much greater economic independence.
Another challenge will be maintaining ideological unity and support in the face of citizens' increased access to the internet and social media. Dissidents have been using social media to stage anti-government protests and gather live audiences online.
In response, the party has said one of the functions of its congress would be "confronting political and ideological subversion, which has made internet and social media its principal field of operations".
But despite the change in leadership, few expect it will prompt a dramatic change in policy direction.
A new constitution in 2019 confirmed state dominance of the economy and the "irrevocability of socialism".
In a tweet on Friday, 60-year-old President Díaz-Canel said the congress would be where "ideas are entrenched, history recognized and the future discussed." But he added that there would be "continuity".
Castro told the congress he was retiring as "a simple revolutionary fighter".
"And as long as I live I will be ready with my foot in the stirrups to defend the fatherland, the revolution and socialism."