The Old Man, whose name is Santiago, is an impoverished but highly skilled fisherman originally from the Canary Islands. He lives alone in a small shack equipped with a bed, a table, and a chair. Decades of working under the sun have left him with deep wrinkles and skin damage, while handling heavy fishing lines has given him deeply scarred hands. He sustains himself on a meager diet, drinking a daily cup of shark liver oil and eating turtle eggs for strength. Despite a deeply unlucky streak of 84 days without a catch, he maintains clear eyes and a resilient spirit. He relies on his precise fishing techniques and the physical endurance developed during his youth as an arm-wrestling champion in Casablanca. He dreams frequently of lions on the beaches of Africa, finding peace in these memories rather than thinking of his deceased wife or past catches.

The Boy, named Manolin, is a young Cuban fisherman who learned his trade directly from The Old Man. When The Old Man's unlucky streak hit 40 days, The Boy's father forced him to work on a more successful, luckier boat. He remains fiercely loyal to his mentor, visiting The Old Man every evening to help carry the heavy mast, furled sail, and harpoon up the hill to his shack. He acts as a compassionate caretaker, buying The Old Man beer at the Terrace restaurant and ensuring he has fresh bait and sardines for the next day.

The Marlin is a gigantic, 18-foot apex predator of the deep ocean, featuring a long, sword-like snout and a massive dorsal fin. Hooked far off the coast of Cuba in the deep waters of the Florida Current, the enormous fish possesses incredible strength and serene determination. It serves as a formidable adversary, pulling a small skiff steadily northward and eastward rather than panicking or thrashing. The fish demands the absolute limits of human endurance, forcing a prolonged physical standoff.

Joe DiMaggio is a star player for the New York Yankees during the 1949 Major League Baseball season. Though he never physically appears in the story, he serves as a powerful psychological presence. DiMaggio is famous for playing brilliantly despite the severe, chronic pain of a bone spur in his heel. The Old Man follows his career closely through newspaper reports and radio broadcasts, using the athlete's resilience as a mental benchmark for his own physical struggles.

Martin is the owner of the Terrace restaurant in the small Cuban fishing village. He operates the local hub where fishermen gather to drink beer, discuss their catches, and observe the ocean. Recognizing The Old Man's severe run of bad luck and resulting poverty, Martin quietly provides high-quality meals to keep the aged fisherman healthy.

Pedrico is a working member of the local Cuban fishing community. He maintains and operates fish traps along the coast. He relies on the leftover parts of large deep-sea catches, chopping up the heads and undesirable meat to use as bait for his own traps.