Billionaire Gautam Adani has once again overtaken oil and petrochemicals magnate Mukesh Ambani to become India's richest man, reclaiming a title that has seesawed between the two tycoons over recent months.

But the battle for supremacy in Asia is no longer just an Indian affair. Both men are now being challenged by Japanese technology investor Masayoshi Son, the founder of SoftBank, whose fortunes have been lifted by the global artificial intelligence boom.

In recent weeks, Son briefly overtook both Adani and Ambani to claim the title of Asia's richest man before falling back again as markets fluctuated.

The shifting rankings underline how closely the fortunes of Asia's wealthiest individuals are tied to stock market movements. Small swings in the share prices of their flagship companies can add or erase billions of dollars from their personal fortunes in a matter of days.

Adani has edged past Ambani over the last few days and is now worth an estimated $89.3 billion. That puts him narrowly ahead of Ambani, who was valued at $88.1 billion by Forbes magazine on Friday. Forbes is widely regarded as the world's leading tracker of billionaire wealth.

The figures vary considerably depending on the methodology used. The Bloomberg Billionaires Index estimates Adani's fortune at around $115 billion, placing him well ahead of Ambani, whose wealth it calculates at $85.8 billion.

Son's wealth climbed sharply earlier this week as Japan's benchmark Nikkei 225 Index surged. At one point Forbes estimated his net worth at around $100 billion, enough to propel him ahead of both Indian billionaires.

The rally also elevated SoftBank above Toyota to become Japan's most valuable listed company by market capitalisation, ending more than two decades of dominance by the automotive giant. Toyota had held the top spot for 23 years.

Japan's stock market has been one of the biggest beneficiaries of investor enthusiasm for artificial intelligence. The Nikkei has risen roughly 30 per cent this year, driven largely by companies linked to AI and advanced technology. SoftBank has substantial exposure to the sector through investments in OpenAI, the company behind ChatGPT, helping drive its share price higher.

However, the wealth rankings remain highly volatile. By Friday, Forbes estimated Son's fortune had slipped back to about $87 billion as technology shares retreated.

Adani's resurgence follows a strong recovery in the value of his listed companies. Shares across the Adani Group have added roughly $10 billion in market value since May 19, when the US Department of Justice moved to drop criminal fraud charges against Gautam Adani and his nephew Sagar Adani, citing insufficient evidence. The decision still requires approval from a federal judge.

Earlier this year, Adani hired prominent US lawyer Robert Giuffra to represent him. Giuffra has also acted as personal counsel to US President Donald Trump.

Investors have also been encouraged by progress at the group's renewable energy businesses.

Adani Green Energy shares have climbed more than 7 per cent over the last five days and are approaching a 52-week high. A key driver has been the commissioning of a new 50-megawatt solar power project at the vast Khavda Renewable Energy Park in Gujarat's Kutch desert, which is expected to become one of the world's largest renewable energy developments.

Adani Green is aiming to more than double its renewable energy capacity from 19.3 GW today to 50 GW by 2030 while “battery storage is becoming the next growth engine, allowing Adani Green to sell electricity at premium night-time prices” instead of much cheaper daytime rates, says a report by US investment bank Jefferies.

The company plans to expand battery storage more than threefold, from 3.4 GWh today to over 10 GWh, with a long-term target of 50 GWh.

Other group companies have also performed strongly. Adani Power shares have risen about 67 per cent over the last six months. “Adani Power has captured nearly two-thirds of all thermal power contracts awarded in India over the past two years.

The company plans to more than double its generating capacity to 42 GW by FY32, cementing its position as India’s largest private thermal power producer,” analysts at Jefferies says.

Analysts also continue to highlight growth prospects at Adani Energy Solutions as India expands its electricity transmission network to meet rapidly rising power demand. Jefferies expects Adani Energy Solutions to grow more than twice as fast as state-run Power Grid over the next five years. Data centres could become a major new source of demand for Adani’s energy solutions business.

Ambani's Reliance Industries, by contrast, has faced a more difficult period. The conglomerate's shares have fallen around 16 per cent over the past six months as investors weighed the impact of turmoil in the Middle East.

Higher shipping costs, elevated insurance premiums and supply chain disruptions linked to tensions around the Strait of Hormuz have added pressure to the company's energy and petrochemicals businesses.

Son's rise has been driven largely by his willingness to make enormous bets on emerging technologies. Over the years he has built a reputation as one of the world's most aggressive venture capital investors.

His latest focus is artificial intelligence. SoftBank has committed tens of billions of dollars to AI-related investments, including a major stake in OpenAI, reflecting Son's conviction that artificial intelligence will reshape the global economy.

The Japanese billionaire is also known for his flamboyant personality. An avid golfer, he reportedly installed an electronic golf range in the basement of his home capable of recreating weather conditions from some of the world's most famous courses. According to one story, he once impressed Microsoft founder Bill Gates by activating a system that produced a light rain shower from the ceiling.

Yet some investors remain cautious. While Son's bold investment style has generated spectacular gains at times, it has also produced painful losses when markets turn. Recent fluctuations in SoftBank's share price reflect lingering concerns about the risks associated with concentrating massive investments in a handful of fashionable sectors.

Adani was briefly the world’s second-richest person worth an estimated $154 billion in late 2022. That put him ahead of Amazon’s Jeff Bezos and LVMH's Bernard Arnault. He was, of course, far behind Elon Musk, the world’s richest man at the time, who was worth $265 billion then. Musk is still ahead in the wealth stakes and is now worth a staggering $820 billion.

Adani’s wealth levels crashed precipitously with the publication of the Hindenburg Report in January 2023, which accused the group of “brazen” stock market manipulation and fraud, allegations the billionaire strongly denied. He has been building back the valuations of his companies since then.

With stock markets being buffeted by everything from AI enthusiasm to geopolitical tensions, the title of Asia’s richest man could change hands several more times before the year is out.