1. Robert Mugabe, Zimbabwe

Robert Mugabe turns 91 this weekend, but the real milestone for the Zimbabwean leader came last summer. When Shimon Peres stepped down as Israel’s president last July, Mugabe assumed the mantle of the world’s oldest head of state.

But he shows no sign of going anywhere. Despite persistent rumours about his health and repeated challenges from within and without, Mugabe has clocked up almost 35 years in power and doesn’t face voters again until 2018.

1. Queen Elizabeth II, United Kingdom

Not just venerable, but also the second longest-serving head of state. When Queen Elizabeth, 89 in April, assumed the throne in 1952, most members of the current cabinet hadn’t even been born, some foodstuffs were still rationed and the Guardian still didn’t have a website.

With one notable exception, being British monarch is a job for life. Plenty have put money on Her Majesty voluntarily stepping down but it’s a bet that never pays out, no matter how many generations of Windsors are awaiting their turn.

1. Beji Caid Essebsi, Tunisia

The top job came to Essebsi late in life — he turned 88 at the end of last year. But he has spent half a century in and around the corridors of power in Tunis and a long career based on pragmatism culminated in his investiture on New Year’s Eve 2014.

Under his stewardship, Tunisia remains the sole Arab spring country to have piloted a course towards democracy and security.

1. Abdul Halim of Kedah, Malaysia

The 87-year-old may also have the longest name of any head of state, going by the formal moniker Almu’tasimu Billahi Muhibbuddin Tuanku Alhaj sir Abdul Halim Mu’adzam Shah Ibni Almarhum Sultan Badlishah.

Raul Castro / Akihito

Under a unique system maintained since 1957, nine hereditary state rulers take turns as the country’s king for five-year terms. The monarch’s role is largely ceremonial, since administrative power is vested in the prime minister and parliament.

1. Bhumibol Adulyadej, Thailand

The Thai king is not the oldest head of state, but he is the longest-serving, have ascended to the throne in 1946. Lese-majesty laws in Thailand make it perilous work to write anything about the ageing monarch. So we won’t.

1. Sabah al-Ahmad al-Jaber al-Sabah, Kuwait

The 85-year-old is the fifth emir of Kuwait, having been sworn in nine years ago. He was previously foreign minister for 40 years, including during the Iraqi invasion in 1990.

1. Raul Castro, Cuba

At 83, he has been in charge of Cuba for almost a decade, after the indisposition of his elder brother Fidel. A more staid presence than the revolutionary leader, Raul also served as armed forces minister for almost 50 years, a record. Unlikely to make it to the top of this list though: he has hinted he will step down in 2018.

Robert Mugabe / Paul Biya

1. Paul Biya, Cameroon

One of the longest serving elected heads of state in the world (however manipulated those elections have been), Biya is 82 has already done 33 years in the job and is set to stay in power for at least another five years.

1. Akihito, Japan

Akihito, 81, acceded to the throne after the death of his father, Hirohito, in 1989. As emperor his duties are largely ceremonial, consisting principally of state visits and apologising to other Asian countries for Japan’s wartime conduct. Possibly the only world leader to have published academic papers about fish.

1. Salman bin Abdulaziz Al Saud, Saudi Arabia

By the standards of this list, Salman bin Abdulaziz Al Saud is something of a new kid on the block, still in his 70s and only recently ascended to the throne. Salman is the latest son of the kingdom’s founder Abdulaziz ibn Saud to accede to the top job. He succeeded his brother Abdullah bin Abdulaziz , who himself ranked second on this list until his death in January.

By arrangement with the Guardian

Published in Dawn February 22nd , 2015

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