Tongan Prime Minister ‘Akilisi Pohiva, who helped wrest power from the royal family and bring greater democracy to the small Pacific island nation, has died.

Mr Pohiva, 78, died on Thursday at the Auckland City Hospital in New Zealand after suffering from pneumonia.

“He will be remembered as the champion of democracy and being primarily responsible for the democratic reforms that were incorporated into the country’s constitution in 2010,” political adviser Lopeti Senituli said.

Mr Pohiva was also known for his fight against global warming.

I mourn the passing of Tongan PM ʻAkilisi Pōhiva, who inspired the world with raw emotion at last month's Pacific Islands Forum in Tuvalu (which, despite his health, he attended in recognition of the urgency of climate action). We must honour his legacy by continuing this fight. pic.twitter.com/MRHysVAaDU — Frank Bainimarama (@FijiPM) September 12, 2019

Archipelagos like Tonga, which is made up 171 islands and is home to 106,000 people, are particularly vulnerable to rising seas.

He spent more than three decades in office after he was first elected to Tonga’s parliament in 1987.

In 2013, he became the first Pacific Islander to win the Defender of Democracy Award, presented by New York-based nonprofit Parliamentarians for Global Action.

“His political career has been marked by battles with the Tongan monarchy over democracy, transparency and corruption,” the non-profit organisation wrote, noting that he was imprisoned in 1996 for contempt of parliament before the Supreme Court ordered he be released.

Regionally, and globally, he will be tremendously missed

“He was an immensely significant figure,” said Graeme Smith, a research fellow at Australian National University.

“As Prime Minister, he was very influential in the region and a really strong voice for Tonga. Regionally, and globally, he will be tremendously missed.”

READ MORE US Supreme Court allows broad enforcement of asylum limits

Mr Smith said it may be too early to tell if Pohiva has created a permanent legacy of strong democracy in Tonga, because there continues to be push back from vested interests including the royal family and the nobility.

For now, politician Semisi Sika is Tonga’s acting prime minister. The Duke and Duchess of Sussex met Tongan prime minister Akilisi Pohiva last year (Phil Noble/PA)

Before becoming a politician, Mr Pohiva taught history and sociology at the University of the South Pacific.

His wife Neomai Pohiva died last year and the couple had seven children.

He spoke at a 2006 pro-democracy rally in the capital Nuku’alofa shortly before rioters destroyed much of the city centre.

After that, the country borrowed money from China to rebuild and now owes 108 million dollars (£88 million) to China’s Export-Import bank, equivalent to about 25% of GDP, a level of indebtedness that worries many observers.

Mr Pohiva was first elected prime minister in 2014 and won re-election three years later. His recent tenure was marked by bouts of ill health.

Fijian Prime Minister Voreqe Bainimarama wrote on Twitter that Mr Pohiva “inspired the world with raw emotion” last month at the Pacific Islands Forum in Tuvalu.

He said Mr Pohiva attended despite his poor health because he recognised the urgency of climate change, adding: “We must honour his legacy by continuing this fight.”

- Press Association