Alexander Valterovich Litvinenko (Russian: Алекса́ндр Ва́льтерович Литвине́нко) (30 August 1962 – 23 November 2006) was an officer who served in the Soviet KGB and its Russian successor, the Federal Security Service (FSB). In November 1998, Litvinenko and several other FSB officers publicly accused their superiors of ordering the assassination of Russian tycoon and oligarch Boris Berezovsky. Litvinenko was arrested the following March on charges of exceeding his authority at work. He was acquitted in November 1999 but re-arrested before the charges were again dismissed in 2000. He fled with his family to London and was granted asylum in the United Kingdom, where he became a journalist and writer.

During his time in London Litvinenko authored two books, "Blowing up Russia: Terror from within" and "Lubyanka Criminal Group," where he accused Russian secret services of staging the Russian apartment bombings and other terrorism acts in an effort to bring Vladimir Putin to power. He also accused Putin of ordering the murder of Russian journalist Anna Politkovskaya.

On 1 November 2006 Litvinenko suddenly fell ill and was hospitalised in what was established as a case of poisoning by radioactive polonium-210 and resulted in his death on 23 November. The events leading up to his poisoning and death are a matter of controversy, spawning numerous theories relating to his poisoning and death. The British investigation into his death resulted in a failed request to Russia for the extradition of Andrey Lugovoy whom they accused of Litvinenko's murder, contributing to the further cooling of Russia–United Kingdom relations.