He started life in a prosperous family but later decided the inequalities in Cuba under the former right wing regime there were wrong. Castro became a Marxist-Leninist and overthrew the corrupt Batista regime in Cuba replacing corrupt Capitalism with inefficient Communism.
Good and bad
Castro has done both good and harm, on the good side Castro improved the health of his citizens but on the bad side many prefer to flee his Socialist Utopia. This is partially because of the blockade coming from the U.S. and EU, because of this, many people live under Poverty conditions. During the Cold War Castro and Cuba were seen as something terrible that brought the problems with Communism that Europeans faced to America and because of this the CIA tried many times to kill Castro.
Today with Communism much weakened this is far less a problem. In later years Castro was old and weak and in poor health, he has handed over effective power to his brother Raúl.
A note on propaganda
It must be remembered that, like other communist rulers, the image of Fidel Castro could have easily been tainted with capitalist propaganda. Communism, and communist countries, could have easily been demonized by the American and capitalist media. This is also true for countries, and the leaders of them, that take an anti-American or anti-capitalist stance. In capitalist countries such as the United States, it must be remembered that the plutocrats have a strong incentive to make communism and communists look as horrible as possible, using the mainstream media. This will turn the general populace off from communism. If there were to be a communist revolution in a capitalist country such as the United States, the plutocrats would be under great threat. Presenting communism in a bad light prevents a revolution that would threaten their power from occurring.