Factbox-Who is Dmitry Medvedev, the Russian war hawk who got under Trump's skin?

FILE PHOTO: Dmitry Medvedev, Deputy Chairman of Russia's Security Council and Chairman of the United Russia political party, delivers a speech during the party's congress in Moscow, Russia, December 17, 2023. Sputnik/Yekaterina Shtukina/Pool via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY./File Photo

(Reuters) -Former Russian president Dmitry Medvedev has become embroiled in a tense back-and-forth on social media that prompted U.S. President Donald Trump to announce he had ordered the re-positioning of two U.S. nuclear submarines.

Who is Medvedev, what is his track record and how influential is he?