In pictures: World's longest serving leaders

Recently, Russians voted for Vladimir Putin, to allow him to remain in power for another 16 years, bringing his total time in office to 32 years, becoming Russia's president for life. Russians appeared to have paved the way for Vladimir Putin to stay in power until 2036 by voting overwhelmingly for a package of constitutional change.

Alexander Lukashenko has been the president of Belarus since 1994 and marked 25 years in power last year. The man once deemed "Europe's last dictator", pushed for a new constitution in 1996 that will expand his authority and scrap term limits.

Ayatollah Ali Khamenei is Iran's second supreme leader and its highest authority - he has the final say over all government matters in the country. He has ruled for 31 years. Since then, he has maintained a firm grip on Iran's politics and its armed forces, and suppressed challenges to the ruling system.

Daniel Ortega has been the president of Nicaragua since 2007. He was voted out in 1990. Ortega lost three straight elections before becoming president again in 2007.

Ismaïl Omar Guelleh has been the president of Djibouti since 1999. In 2016, Guelleh won a fourth term. Some opposition parties boycotted the election and criticized as political repression.

Tajikistan’s long-serving ruler Emomali Rahmon has served as the president of Tajikistan since 1994. Rahmon was elected to his second term as president in 1997, and in 2003, a referendum was passed that allowed him to serve two more terms. Rahmon was elected to his second term as president in November 1999. In June 2003, a referendum was passed that made it possible for Rahmon to serve two more consecutive terms after his second term expired in 2006. The election on November 6, 2006, granted Rahmon his third term, but the vote was widely criticized for being neither free nor fair. Re-elected in late 2013, he will now serve in current position until 2021.

Cambodia's Hun Sen has been in power since 1985 and is one of the world's longest-serving prime ministers. He is credited with helping achieve economic growth and peace after the devastation caused by the Khmer Rouge regime, responsible for one of the worst mass killings of the 20th century.

Cameroon's President Paul Biya has been in power for 37 years but is seeking another seven-year term. His longevity in office is a talking point at home. At 87 years old, Biya is the oldest leader in Africa.

Already one of Africa's longest serving leaders, Yoweri Museveni has been the president of Uganda since 1986, and he is expected to enter his sixth term in 2021. Museveni is consistently elected unopposed due to the popular votes in elections.