(Reuters) - Michael Flynn, President Donald Trump’s first U.S. national security adviser, pleaded guilty on Friday to lying to the Federal Bureau of Investigation about his contacts with Russia’s U.S. ambassador. Here are five facts about Flynn:     Flynn was national security adviser for just 24 days, from Jan. 20, when Trump took office, to Feb. 13. Flynn was fired following disclosures that he had discussed U.S. sanctions on Russia with Sergey Kislyak, Moscow’s U.S. ambassador, and misled Vice President Mike Pence about the conversations. On Feb. 14, Trump asked then-FBI Director James Comey in an Oval Office meeting to end the agency’s investigation into ties between Flynn and Russia, according to news media reports. Trump, who fired Comey on May 9, later denied making such a request. Trump had named the former Army lieutenant general to the national security post despite red flags about Flynn’s Russian contacts and advocacy for warmer U.S. relations with Moscow, which has been under U.S. economic sanctions for years. Outgoing President Barack Obama had warned Trump not to hire Flynn, who had been fired by the Democratic president in 2014. Flynn was an early and vociferous Trump supporter during the New York businessman’s 2016 White House run. He made vitriolic appearances on the campaign trail, notably leading the Republican National Convention in chants of “Lock her up,” referring to Trump’s Democratic rival, former Secretary of State Hillary Clinton. In addition to Flynn’s contacts with Russia, Special Counsel Robert Mueller’s investigation of possible ties between the Trump election campaign and Moscow has expanded its probe to include Flynn’s paid work as a lobbyist for a Turkish businessman in 2016, people with knowledge of the inquiry have told Reuters. 