The 50 people who matter today: 11-20

11-20 on our diverse list of individuals, couples and families changing the world, for good and ill.

11. Daniel Nocera

Gas man

In 2004, an epoch-making realisation dawned on the MIT chemist Daniel Nocera. He saw that the photosynthetic mechanisms that plants use to split water could be mimicked in such a way as to build a catalyst capable of making hydrogen fuel. In coming to understand how hydrogen ions could be harnessed to make hydrogen gas, Nocera had happened on a procedure that could conceivably transform the way energy is generated. It is no exaggeration to say that the prospects for genuinely renewable energy in coming decades depend on Nocera's ability to develop a catalyst that runs not on electricity, but on sunlight itself.

12. Angela Merkel

Wunderfrau

A champion of business, Angela Merkel is the first woman to lead Germany since it became a nation state in 1871. And as leader of Europe's largest economy and the world's biggest exporter, she carries huge weight on the international scene. Merkel stands as a bulwark to the Anglo-Saxon capitalist free market. She pushes for tighter international regulation on banks and led the crackdown on bank bonuses that recently cowed Gordon Brown. She is a solid supporter of the invasion of Afghanistan and her back-seat diplomacy has been crucial in brokering compromise between the UK and US. With a personal approval rating of over 60 per cent, Merkel is Europe's most popular leader and the justified proprietor of the Forbes title of "Most Powerful Woman in the World".

13. Bill and Melinda Gates

The softies

Microsoft brought the Gateses their fortune, but nowadays their global influence is felt through their eponymous foundation. It is the largest of its kind in the world, with an endowment worth some $35bn. The $800m that the couple give every year to health programmes tackling diseases such as polio and malaria is almost equal to the World Health Organisation's annual budget. Their philanthropy has attracted others to the cause - Warren Buffett gave roughly $30bn (nearly half his fortune) to the foundation in 2006. But it has also attracted criticism: some suggest that their donations undermine public health systems in developing countries.

14. Paul Kagame

Rwandan unifier

Over a period of 100 days beginning in April 1994, more than 900,000 people, mostly from the country's minority Tutsi group, were slaughtered in the small, landlocked Central-East African country of Rwanda in a state-driven assertion of Hutu supremacy that the rest of the world, turning away in fear and revulsion, did nothing to stop. The failure to intervene in Rwanda was an act of cowardice for which countries such as Britain (which has become the world's largest bilateral donor to Rwanda) and the US have been seeking to atone ever since. The killing was eventually stopped by the Rwandan Patriotic Front, a guerrilla movement that invaded from bases outside the country. Its leader was the Tutsi politician-soldier Paul Kagame. A brilliant military tactician who fought alongside Yoweri Museveni when he toppled Uganda's Tito Okello in a coup in 1986, Kagame was born in October 1957 and grew up in a refugee camp in Uganda. His parents fled from Rwanda during one of the country's periodic and systematic purges of the Tutsi minority. (The Tutsi diaspora is spread across Africa, with large groupings in Uganda, Tanzania, Burundi and the Democratic Republic of Congo.)

To many, the tall, thin, ascetic Kagame is a hero. As president, he has abolished the divisive system of identity cards, introduced by the Belgian colonisers, who first politicised ethnicity in Rwanda and under whose governance each citizen had to carry proof of his or her ethnicity: Hutu, Tutsi or Twa. His minority-Tutsi regime has stabilised and modernised Rwanda, rebuilding the country from the trauma of genocide and the ravages of civil war. His hugely efficient military - arguably the best in Africa - helped to topple the despised Mobutu regime in the country that was then called Zaire.

But to his disparagers, of whom there are increasing numbers, absolute power has corrupted Kagame. He is a hardline authoritarian and war criminal. Rwanda's repeated incursions over the border into eastern Congo have been driven less by a desire to root out Hutu militias than by greed and expansionist ambition. The Rwandan Tutsi elite, it is said, has become rich on the mineral wealth looted from the war-ravaged eastern Congo: cassiterite, gold, coltan.

The war in Congo - Africa's World War, as it is called - has resulted in the death of as many as 5.5 million people; millions, too, have been displaced, and hundreds of thousands of women have been raped. At present it seems to be a war without end, under-reported, misunderstood and shamefully too often ignored by western powers.

Does Kagame have the power to bring peace to eastern Congo? It seems absurd that a country as small as Rwanda could control the fortunes of one as vast as the DRC. But so pervasive is Kagame's influence in the Great Lakes region, so disciplined is the Rwandan military, so determined is the ethnic Tutsi elite (rather like the Jews of Israel) never again to be victims of genocide, and so supportive is the anglophone world of Kagame (to the irritation of the French, who supported the Hutu majority) that this complex and determined politician has, more than any other leader in the region, the authority and opportunity to broker peace in what is one of the most tragic nations on earth.
Jason Cowley

15. David Einhorn

High roller

David Einhorn has had a profound effect on Wall Street. As founder of the hedge fund Greenlight Capital, he was one of the first to see gaps in Lehman Brothers' first-quarter earnings in May 2008. Short-selling Lehman shares, he realised a hefty profit. Last year, he publicly denounced Lehman's shortfall before the Securities and Exchange Commission, the Federal Reserve, or even Lehman's investors did. His gambling prowess was better known on Vegas poker circuits until 2002, when he exposed fraudulent records in the mid-cap financial company Allied Capital. Critics claim he caused a crisis of confidence in the economy, but he has been hugely important in ushering an era of accountability on to Wall Street.

16. Harvey Levin

Gossip guy

TMZ.com, Harvey Levin's website (the acro­nym stands for the "thirty-mile zone" around Hollywood), feeds on celebrity activity of the lowest order: Twitter fights, Starbucks encounters, stylist errors. But it has also scooped some of the biggest celebrity stories since it began in 2005 - this year's trophy was the death of Michael Jackson, and the site's pictures of Britney Spears's meltdown were seen around the globe. In doing so, it has contributed to the increasing redundancy of slow print media. Levin, a lawyer by training, is now a media star in his own right, but it's his network of moles around LA (in the hospital, some said, when Jackson died) that makes the site the most influential source of gossip in the world.

17. Grand Ayatollah Yousuf Sanei

Clerical errant

A rare liberal voice from within Iran's theocratic Establishment, Grand Ayatollah Yousuf Sanei is not afraid of going against the grain: President Mahmoud Ahmadinejad plans to sue the senior reformist cleric for siding with pro-democracy protesters during June's contested elections. Sanei was already known, and well respected, for his progressive fatwas (condemning suicide bombing and nuclear weapons, and promoting women's rights), and holds one of the most senior clerical positions in Shia Islam. In a country so hostile to the west, a real chance of modernisation could only come from someone with his insider status.

18. Francis Collins

Gene genius

For 15 years, as the head of the Human Genome Project, Francis Collins led the quest to unravel the human genome. A born-again Christian, he created the BioLogos Foundation to promote harmony between science and faith. In May, he resigned to explore other avenues; in July, Barack Obama nominated him as director of the National Institutes of Health.

19. Mo Ibrahim

Networker

He made his name and fortune from mobile phones, but Sudanese-born Mo Ibrahim has joined the ranks of global figureheads through his eponymous foundation. When Ibrahim set up his mobile phone company Celtel in 1998, there were two million phones in Africa. Seven years later, there were 100 million, opening up unprecedented business and communication. His foundation promotes good governance in Africa, awarding the largest financial prize in the world ($5m plus $200,000 a year for life) to an African leader every year.

20. Robert Iger

Cartoon hero

As the Walt Disney Company's CEO, Robert Iger is the head of the world's largest media conglomerate. Through entertainment phenomena such as Hannah Montana, he controls the deepest desires of the next generation; he also directs the TV news giant ABC and sports channel ESPN. In 2006, he acquired the digital animation studios Pixar, cemented a relationship with Apple's Steve Jobs and signed a $6bn merger with Marvel comics, adding more than 2,000 characters to Disney's repertoire.