He is also the title character in the first George Smiley continuation novel, Karla's Choice by Nick Harkaway, which is set in the period some time before Tinker Tailor Soldier Spy.
In the BBC's television adaptations of both Tinker Tailor Soldier Spy and Smiley's People, Karla is played by British actor Patrick Stewart.
Among the rumours are that his father was a professional intelligence officer, first for the Czarist Okhranka and later for the Bolshevist Cheka; that as a boy Karla worked as a kitchen boy on a train in occupied Siberia during the Russo-Japanese War of 1904–1905 (putting his birth somewhere in the late 19th century); and that he was trained in espionage by "Berg" (a possible reference to the alias "Igor Konstantinovich Berg" used by Alexander Orlov), which Smiley compares to "being taught music by a great composer.
He traveled to England in 1936 and 1941 and recruited Bill Haydon, code-named "Gerald", who eventually became the number-two man in the "Circus" (the British Secret Intelligence Service).
At another time he recruited Nelson Ko, a high-ranking technocrat in the People's Republic of China (according to Connie Sachs, Karla was one of the few Soviets to predict the souring of Sino-Soviet relations).
[1] After being promoted away from active fieldwork, Karla sought to create his own independent apparatus inside Moscow Centre, believing that his personal agents were too important to leave to others.
He founded a special camp outside Moscow (towards Kyiv) and trained a selection of handpicked men (usually ex-military officers) to act as handlers of his various moles.
By the time of the novel, the mole—Bill Haydon—has become The Circus' number-two man; Karla uses his handler, Alexei Polyakov, to deliver fabricated intelligence that appears highly valuable.
Karla's aggressive targeting of operatives all over the world necessitates the Circus to shut down safe houses and recall spies even in non-Soviet countries, including one in Vietnam.
He is proven right, as evidence of Haydon's refusal to investigate a possible money laundering operation in Laos leads them to unmask Nelson Ko, Karla's mole inside the People's Republic of China.
Although the Circus fails to capture Nelson themselves, their joint cooperation with the CIA leads to the Americans seizing him as he attempts to escape to Hong Kong from mainland China.
His mistress was Estonian, and in his daughter's incoherent memory, Karla had her mother killed after he overheard her praying (contrary to communism's atheist views).
[2] Unable to get her proper treatment, Karla uses a set of amateur agents to find or create a false identity that would allow him to send her to Western Europe to an adequate mental health clinic.
As new Circus Chief Saul Enderby comments, Karla had to use amateurs because he had trained his own agents to be both too smart and too fanatically devoted to his ideals to be trusted with his private scheme.
Roughly a year later, Karla committed suicide; according to Prideaux, Smiley became grief stricken at his death, a response he doesn't understand given the nature of their relationship.
[6] Karla appears briefly in the 2011 film adaptation of Tinker Tailor Soldier Spy as a voice, provided by Michael Sarne, as well as in a partial shot in a Budapest coffee shop holding Smiley's lighter.