TOKYO (BLOOMBERG/AFP) - Japan's Emperor Akihito, who on Wednesday (July 14) signalled his wish to step down in a matter of years, has been credited with helping modernise Japan's monarchy.

The Emperor, 82, has reigned for 28 years, after succeeding his father Hirohito in 1989.

Serving in a strictly symbolic role as prescribed by the US-imposed post-World War II Constitution, Emperor Akihito began his reign as the nation was at the zenith of its economic power and just a year before a "bubble economy" burst, which ushered in decades of economic stagnation.

"This would be huge because Akihito is enormously popular with the public; he is a voice of reconciliation and looks at dealing with the lingering grievances from World War II as his father's unfinished business," said Professor Jeff Kingston, director of Asian studies at Temple University in Japan.

"He has done more than all of Japan's politicians put together in terms of raising Japan's stature in the region - he is known as the people's Emperor."

Kingston said it was likely the decision was driven by the Emperor's advancing age and deteriorating health. Emperor Akihito underwent almost four hours of surgery for a successful heart bypass in 2012, and was hospitalised for pneumonia the previous year. Crown Prince Naruhito served as regent while his father was recovering.

The Emperor also had prostate surgery in 2003.

"I am beginning to feel my age, and there were times when I made some mistakes at events," he told reporters at an annual press conference just ahead of his birthday on Dec 23.

In visits across Asia and beyond, Emperor Akihito addressed the issue of the past aggression Japan's military carried out in his father's name.

In 1990, he apologised for Japan's colonisation of Korea from 1910 to 1945. Two years later, during the first visit by a Japanese monarch to China, he acknowledged that Japan had "inflicted great suffering" on its neighbour in the first half of the century.

In a speech last year to mark the 70th anniversary of the end of World War II, Emperor Akihito expressed "deep remorse" over his country's actions in the conflict. The remarks - his first such expression of regret since coming to the throne in 1989 - contrasted with those of Prime Minister Shinzo Abe, who said in a statement at the time that Japan should not be expected to continually apologise.

A scientist by avocation, Emperor Akihito is the first royal heir to have married a commoner, Empress Michiko Shoda, the daughter of a wealthy industrialist. The two met on a tennis court and their 1959 marriage was a national sensation.

Emperor Akihito will be succeeded by his eldest son, Crown Prince Naruhito, who is 56.