What you need to know:
- Belarus President Alexander Lukashenko, 69, a close ally of Putin, has used Soviet-style repression to remain in power in Ukraine's neighbour for 29 years.
- In Russia, 71-year-old Putin has been leader since December 1999.
Vladimir Putin, who on Friday announced that he will seek a fifth term as Russian president in elections next year, is one of the world's ten longest-serving elected leaders.
Here are the top 10, ranked by total number of years in power.
Equatorial Guinea's Obiang: 44 years
The Soviet Union was still a decade from collapse when Teodoro Obiang Nguema, 81, came to power in a coup in the west African state of Equatorial Guinea in 1979.
Under his repressive 44-year rule, Equatorial Guinea has become known as the "North Korea of Africa".
Cameroon's Biya: 41 years
The world's oldest elected leader, 90-year-old Cameroonian President Paul Biya, has ruled his west African country with an iron fist since November 1982.
Nicknamed "the Sphinx" for his inscrutable nature, he won a seventh consecutive term in 2018 after elections marred by allegations of fraud.
Congo-Brazzaville's Sassou Nguesso: 39 years
Republic of Congo (also known as Congo-Brazzaville): Denis Sassou Nguesso, 80, has spent 39 years at the helm of the country in central Africa. He was president from 1979 to 1992, then returned in 1997 after a civil war and has remained in power ever since.
Uganda's Museveni: 37 years
Ugandan President Yoweri Museveni, 79, has led the central African country for 37 years. He was re-elected to a contested sixth term in 2021 elections.
Tajikistan's Rahmon: 31 years
Tajikistan: Emomali Rahmon, a 71-year-old former collective farm boss who came to power shortly after the collapse of the Soviet Union, has had a firm grip on his poor, mountainous country for 31 years.
Eritrea's Afwerki: 30 years
Former rebel leader Isaias Afwerki, 77, has been president of the reclusive Horn of Africa nation of Eritrea since it won independence from Ethiopia in 1993.
Belarus's Lukashenko: 29 years
Belarus President Alexander Lukashenko, 69, a close ally of Putin, has used Soviet-style repression to remain in power in Ukraine's neighbour for 29 years.
Djibouti's Guelleh: 24 years
Djibouti's President Ismail Omar Guelleh, 76, who was re-elected to a fifth term in 2021, has been leader of the country that styles itself the "Dubai of Africa", for 24 years.
Russia's Putin: 24 years
In Russia, 71-year-old Putin has been leader since December 1999.
He became acting president in December 1999, then served two terms from 2000 to 2008 before swapping jobs with his prime minister Dmitry Medvedev to circumvent rules limiting consecutive presidential mandates to two, only to reclaim the role of Kremlin leader in 2012.
Term limits would have disqualified Putin from standing in the next election but a controversial constitutional reform in 2020 paved the way for him to stay in power until at least 2036.
Rwanda's Kagame: 23 years
Rwandan President Paul Kagame, a former Tutsi rebel leader who put an end to a genocide of Tutsis in 1994, has been president of the small central African republic since April 2000.