Nicholas Salmanovitch Rubashov fought in the revolution that brought communism to Russia. He then became a functionary of the Communist Party, a job that frequently involved denouncing those who did not unquestioningly support Party ideology. As a member of the Old Guard of revolutionaries, Rubashov believes in the individual as a moral member of the collective. The new Party no longer believes in individuals and sacrifices them for its own ideological aims. Thus Rubashov is viewed as an opponent of the new Party, and he's arrested. He is interrogated in prison and coerced into confessing to treasonous opposition to the Party, as well as to plotting to assassinate the dictator, No. 1. He finally does admit to all the crimes of which he is accused and is executed.
Gletkin comes from uneducated peasant stock and is an immovable proponent of the new Party ideology. In his 30s, he is younger than Rubashov. Gletkin has no understanding of history, of the revolution, and especially of the Old Guard. Gletkin is crude and a brute, but he's adept at using twisted Party logic to force Rubashov to accept the new Party ideology, which denies the existence of the individual and of morality. For Gletkin, anti-Party thoughts are as incriminating as anti-Party acts. If Rubashov had doubts about No. 1, it follows logically that he must have plotted the assassination of No. 1. Gletkin's twisted logic eventually forces the exhausted Rubashov to confess to everything the Party demands of him, including plotting to kill No. 1.
Ivanov is an old friend of Rubashov's from the time of the Old Guard. He doesn't truly believe Rubashov is guilty of all the charges against him, but as an official in the new Party, Ivanov argues logically with Rubashov to get him to confess. Ivanov wants Rubashov to confess in order to please the Party by embracing its new ideology. At first Rubashov refuses to confess and bend to the new Party ideology. Later, however, Rubashov does "capitulate," signaling his intention to confess at some later time. Ivanov's soft approach to interrogating Rubashov ends up costing him his life.
Hare-lip, whose real name is Michael Kieffer, is held in a cell on the same prison corridor as Rubashov. Rubashov knows very little about him until he's brought into one of Gletkin's interrogations. Rubashov sees that Hare-lip has been tortured or beaten. The reason for this mistreatment becomes clear when Hare-lip identifies himself as Michael Kieffer, the son of an Old Guard friend of Rubashov's. Hare-lip's testimony regarding a conversation he'd had with Rubashov incriminates Rubashov in a plot to assassinate No. 1. Although the conversation was mainly about Rubashov's doubts about No. 1, this is still sufficient to condemn him. Hare-lip had hoped his testimony would save his life, but he, too, is condemned for the same treason as Rubashov.
Little Loewy is a Party member and union leader of dockworkers at a port in Belgium. He wholeheartedly supports the Party until he learns from Rubashov of its deception and betrayal of the workers. Even though he says nothing about his disagreement with the Party's decision to undermine the workers for its own benefit, Little Loewy is denounced by Rubashov for his oppositional thoughts. Little Loewy is likely murdered by the Party for his views and unspoken disagreement.
Richard is a very young leader of a communist cell in an unnamed European country (probably Germany). Richard changes the wording in the pamphlets his cell members hand out to the public. He gets rid of the lies in the Party-approved pamphlets and replaces them with truthful words. Rubashov, as a Party official, deems this action oppositional and traitorous to the Party. Rubashov denounces Richard, who is no doubt arrested and executed.
402 is the prisoner occupying the cell adjacent to Rubashov's. The two often communicate via tapping on the wall between them. 402 is serving a very long prison sentence for being a monarchist, or supporter of the tsar. Although at first 402 reviles Rubashov for his work for the Party, eventually they find common ground. 402 has clear and humane ideas about honor, decency, and the morality of the individual. In time Rubashov comes to agree with these ideas, and 402 starts to support Rubashov in his evolution to a more humane, anti-Party outlook. When Rubashov informs 402 he will capitulate to the Party's demand that he confess, 402 almost breaks their growing friendship.