Jean-Claude Duvalier, a former president of Haiti known as Baby Doc who ruled the country with a bloody brutality and then shocked it anew with a sudden return from a 25-year exile in 2011, died on Saturday.

Mr. Duvalier, 63, died of a heart attack in Port-au-Prince, Haiti, at a private residence where he was staying, his lawyer told The Associated Press. President Michel J. Martelly announced the death on Twitter.

Mr. Duvalier continued to defend what human rights workers called one of the most oppressive governments in the Western Hemisphere, following in the footsteps of his father, François, known as Papa Doc, who died in 1971. The son was 19 when he assumed the post “president for life,” as he and his father called it, becoming the youngest head of state at the time.