Qatar Investment Authority
The investment arm of the state of Qatar. QIA is estimated to control more than £30bn, putting it in the top 10 most powerful sovereign wealth funds.
Its investments include a 25% stake in J Sainsbury, following last year's failed attempt to take the supermarket chain over. It holds a large stake in the London Stock Exchange, and is leading a £1bn consortium to redevelop London's Chelsea Barracks.
The group also owns the Four Seasons nursing home chain, although it is reportedly trying to find a buyer.
Like all sovereign wealth funds, QIA shuns the spotlight. It recently parted company with Paul Taylor, the UK financier who led the Sainsbury's bid.
Challenger Universal Limited
Specially created earlier this month to hold shares in Barclays, Challenger represents the financial interests of Sheikh Hamad Bin Jassim Bin Jabr Al-Thani and his family.
Sheikh Hamad is both the prime minister and the foreign minister of Qatar, and reportedly the state's second richest person. He is said to have a good relationship with the White House, reflecting the importance of the country's reserves of oil and gas.
Temasek Holdings
The investment arm of the government of Singapore. It was founded in 1975 to handle the administration's stakes in a range of companies, and now manages more than £50bn.
Temasek already held a 2.1% stake in Barclays, having invested last July – and incurred significant paper losses as the UK bank's shares kept falling since. It is also nursing a loss having invested billions of dollars in Merrill Lynch.
In 2006, there were riots in Thailand after Temasek bought Shin Corporation, a conglomerate owned by the family of then Thai prime minister Thaksin Shinawatra.
After Shinawatra was overthrown later that year, the military rulers that replaced him ordered Temasek to sell the stake, although it still appears on its list of investments.
China Development Bank
It reports to the Chinese government, with a remit to lend money to drive development – particularly new infrastructure – across China.
Much of its funding comes from the Chinese government, and is then distributed in thousands of loans. Thanks to the booming economy, it now has the muscle to buy stakes in some of the West's largest companies.
In February it bankrolled Chinalco, the state-owned aluminium group, when it snapped up a 12% stake in Rio Tinto in a surprise stock market swoop.
Like Temasek, it has been an investor since last summer when it bought 3% of Barclays.
Sumitomo Mitsui Banking Corporation
Japan's third-largest bank is looking to build stakes abroad to make up for the lacklustre prospects in its domestic market.
Based in Tokyo, it employs almost 18,000 people around the world – with offices in Asia, Europe, Africa and the Middle East.
Like other Asian banks, it has been less affected by the credit crisis than US and European financial institutions. Ratings agency Standard and Poor's recently urged Japanese banks to raise their overseas investments,
Its history dates back to the 1870s, and like most banks it has grown through a series of mergers and acquisitions since.
Rumours of Sumitomo's interest in Barclays emerged last week.
