Alexander Litvinenko was a former officer of the Russian Federal Security Service (FSB) who became a vocal critic of the Russian government. He fled to the United Kingdom in 2000, where he sought asylum and continued to speak out against corruption and human rights abuses in Russia. In November 2006, Litvinenko fell seriously ill and died three weeks later. His death was attributed to poisoning with polonium-210, a rare radioactive substance. The circumstances surrounding his death led to international investigations and heightened tensions between the UK and Russia.