George Smiley is an aging, highly observant former spy forced into an early pension following the disastrous Operation Testify in Czechoslovakia. He passes his days in London practicing memory exercises to keep his mind sharp, while quietly enduring the public humiliation of his wife's frequent affairs. Despite his mild and unassuming exterior, he possesses a brilliant analytical mind that prompts the British government to secretly re-recruit him to find a suspected Soviet mole.

Bill Haydon is a high-ranking intelligence officer who cultivates the persona of a detached artist and intellectual. He runs the London station and forms part of the inner circle overseeing Operation Witchcraft, a secretive new intelligence pipeline. He possesses a sardonic wit and an undeniable charisma that draws fierce loyalty from his subordinates and colleagues alike.

Percy Alleline is the ambitious new chief of the Circus. He leverages high-level political connections and conservative backers to oust his predecessor and secure the top leadership position. He aggressively champions Operation Witchcraft, treating the secretive Soviet intelligence source as his personal triumph and a means to solidify his authority.

Jim Prideaux is a physically scarred former intelligence agent who survived capture and torture during the failed Operation Testify in Czechoslovakia. He now lives out of a caravan at a quiet prep school, projecting a tough, outdoorsy demeanor that masks severe emotional trauma. He feels a deep sense of betrayal toward the country and institutions he once faithfully served.

Karla is a legendary, shadowy Soviet intelligence mastermind. He operates with absolute ideological devotion and silence, rarely leaving traces of his involvement. He haunts the British intelligence agents as a terrifying symbol of ruthless efficiency and long-term strategic plotting.

Control is the secretive former head of British intelligence who died in disgrace shortly after his dismissal. Before his fall, he launched the disastrous Operation Testify in a frantic, off-the-books bid to uncover a suspected Soviet mole. He operated with intense autonomy, keeping his true name hidden and trusting almost no one in his final, paranoid days.

Peter Guilliam is a resourceful intelligence officer currently demoted to running the "scalphunters," a division handling violent or messy field operations. Following the agency shakeup, he feels alienated from the new leadership. He acts as Smiley's clandestine operative, stealing documents and monitoring internal communications at immense personal risk.

Toby Esterhase oversees the practical aspects of wiretapping and physical trailing for British intelligence. Originating from Hungary, he adopts flamboyant clothes and exaggerated English mannerisms in a desperate attempt to fit into the upper-class British establishment. He is fiercely concerned with his own survival within the shifting power dynamics of the agency.

Roy Bland is a former left-wing academic recruited into the intelligence service from a working-class background. He utilizes his extensive knowledge of communist literature to translate and analyze Soviet intelligence. Years of spy work have drained his youthful ideological passion, replacing it with a detached, cynical pragmatism.

Oliver Lacon is a civil servant who acts as the primary liaison between the British government and the intelligence agencies. He represents the establishment's cautious, bureaucratic approach to state secrets. Panicked by the prospect of a high-level mole, he relies on Smiley's expertise to quietly investigate the Circus from the outside.

Bill Roach is a lonely, anxious young boy starting his first term at an English private school. He carries heavy guilt over his wealthy parents' recent divorce, which alienates him from his peers. He finds an unexpected connection with the new substitute teacher, learning to carefully monitor the world around him.

Ann Smiley is an aristocratic woman whose frequent infidelities are an open joke among her husband's social circle. Though she remains off-page for most of the story, her actions cast a long shadow over Smiley's life and professional relationships, functioning as his singular emotional vulnerability.

Ricki Tarr is an emotional, slightly reckless field agent who specializes in rough operations in British colonies. Officially listed as a defector after disappearing in Hong Kong, he resurfaces with claims of a high-level Soviet mole. He desperately seeks validation and protection from his former recruiters.

Connie Sachs is a brilliant former research analyst forcibly retired from the Circus. She possesses an encyclopedic memory of Soviet agents and operations. Living in relative poverty, she deeply misses the thrill of spy craft and resents the male superiors who dismissed her accurate suspicions regarding Russian operatives.

Aleks Polyakov is a Soviet official operating in London under a diplomatic cover. Despite his civilian records, Connie Sachs suspects him of being a highly trained military intelligence operative. He acts as a crucial intermediary between Russian spymasters and British sources.

Irina is a Soviet intelligence courier trapped in a miserable common-law marriage with another agent. She possesses explosive knowledge about a mole in British intelligence and attempts to leverage this information to secure a defection to the West.

Boris is an inept Soviet intelligence agent assigned to Hong Kong. He spends most of his time drinking and pursuing women, alienating his partner and drawing unnecessary attention from foreign surveillance teams.

Roddy Martindale is an obsequious government acquaintance who relishes political gossip. He uses his dinner with Smiley to fish for details about Control's downfall and the new leadership, representing the idle chatter of the London bureaucratic class.

Jerry Westerby is a journalist and former Circus employee. He utilizes his press credentials to travel through Eastern Europe, accidentally stumbling upon military inconsistencies regarding the failed British mission in Czechoslovakia.

Sam is a former Circus duty officer fired after being caught drinking at work. He now works for a gambling firm but provides Smiley with a detailed account of the chaotic night the Czechoslovakia mission fell apart.

Max is a former intelligence operative who provided ground support for Prideaux in Czechoslovakia. He waited in a hotel under a fake Austrian identity while the mission collapsed, eventually returning to Britain to find himself suddenly unemployed.

Mendel is a retired police inspector who provides off-the-books logistical support for Smiley's investigation. He tracks down addresses, runs surveillance outside the Circus, and manages safe houses, operating with quiet, dependable efficiency.