From Wiki:
Abramovich was the first person to recommend to Yeltsin that
Vladimir Putin be his successor as the Russian president.
[50]: 135 When Putin formed his first cabinet as Prime Minister in 1999, Abramovich interviewed each of the candidates for cabinet positions before they were approved.
[33]: 102 Subsequently, Abramovich would remain one of Putin's closest confidants. In 2007, Putin consulted in meetings with Abramovich on the question of who should be his successor as president; Medvedev was personally recommended by Abramovich.
[50]: 135, 271
Chris Hutchins, a biographer of Putin, described the relationship between the Russian president and Abramovich as like that between a father and a favourite son. Abramovich has said that when he addresses Putin he uses the Russian language's formal "вы" (like Spanish "usted", German "Sie", Italian "lei" or French "vous"), as opposed to the informal "ты" (Spanish "tú", German "du", Italian "tu" or French "tu"). Abramovich says that the reason is 'he is more senior than me'.
[51] Within the Kremlin, Abramovich is referred to as "Mr A".
[52]
In May 2018, Abramovich became an Israeli citizen a month after the UK delayed renewing his visa. In April 2021, Abramovich became a Portuguese citizen as part of the Nationality Act due to his reported Sephardic Jewish heritage.