Final answer:
Fidel Castro was the longest running leftist leader in Latin America, governing Cuba from 1959 until he ceded power to his brother in 2006.
Step-by-step explanation:
The longest running leftist leader in Latin America was Fidel Castro of Cuba. Cuba emerged as the lone Communist state in the Americas at the turn of the 21st century, with Castro being the longest-governing leader of any country in the world. Despite his initial promises, Castro did not hold free elections, but instead suppressed free speech and exercised control over the state until he turned over power to his brother Raúl in 2006. Examples of other leftist leaders, although not matching Castro's longevity, include Salvador Allende of Chile and Daniel Ortega of Nicaragua, but their tenures were significantly shorter due to coups and opposition.