Businessman and philanthropist Bill Gates talks with IMF Managing Director Christine Lagarde at the G-20 summit. (Charles Dharapak/AP)

Organizations representing the world’s poor have had a fitful relationship with the Group of 20 world leaders. They arrive en masse to hold news conferences and usually get a nice mention of food security and health in any communique, but they mostly see their larger aims shoved aside by whatever crisis has hit major banks or currencies.

Enter Bill Gates, literally.

In what may mark a signature breakthrough, the Microsoft chairman and Gates Foundation philanthropist was given 90 minutes before a group that’s become a kind of executive board for the global economy.

Given events around the world — the trouble roiling Greece and the dense agenda of financial issues the group aimed to tackle — the amount of time in itself was extraordinary.

This was no courtesy call on a head of state. It was a nuts-and-bolts discussion with the world’s collected leaders — President Obama, China’s Hu Jintao, Europeans, Brazilians and South Koreans — about ways Gates thinks they can do more to help the poor.

He even earned a mention by name in the final communique.

“I was a bit nervous,” said Gates, whose eponymous foundation has become the conduit for one of the world’s largest personal fortunes. He took up the first 12 minutes talking about ways to leverage science and smarter organization into productivity gains for local farmers and better health outcomes in poor communities.

Then they bantered for more than an hour.

“It was an amazing opportunity to articulate the importance of innovation,” Gates said. “All these leaders want to have a personal legacy of having done positive humanitarian things. Showing them a path where, given all the constraints they operate under, there really is an opportunity — it was daunting . . . unprecedented.”

In these days of Occupy Wall Street, Occupy D.C. — Occupy Peoria for that matter — the G-20 is at more than the usual risk of an image problem. Gathering in Cannes, on the French Riviera, doesn’t help.

It’s great for security: a seafront harbor that’s easy to police from the water side, and with one or two main roads cut off, it makes an instant enclave. Shop owners seem to have vacated — many stores are closed — and the residents have made themselves scarce. A man with a feather boa and crown managed to break into the media area Thursday, but the only other hint of protest has been in faraway Nice.

But if there was ever a clashing image, it is that of leaders such as German Chancellor Angela Merkel lecturing the people of Greece on their struggling economy from the village where the world’s stars and starlets gather each year to flaunt their money and show their new movies to each other.

And yet, anti-poverty advocates say the Gates visit may be a game changer. Groups such as Oxfam consulted with the Gates Foundation about the report, “Innovation with Impact,” that Gates presented to the heads of state. Having him invited into the room at Cannes, they hope, will give their issues a more forceful presence in the future.

“It is surprising how civil society has embraced Bill Gates as their champion,” said Samuel A. Worthington, president of InterAction, an anti-poverty lobby. “That report to the group has been our only real hook” on development and poverty issues at the summit.

Gates said talk is already underway about a follow-up meeting, focused on agricultural research, next year when the G-20 presidency and summit shifts to Mexico.

It was in some ways an accidental gathering. The invitation stemmed from a meeting this past spring between French President Nicolas Sarkozy and Gates over the work the foundation has done on issues such as polio eradication and boosting crop yields.

This year’s G-20 chairman, Sarkozy wanted food issues on the agenda. He also wanted to push for a tax on financial transactions and saw Gates as a way to serve both ends.

What about a transaction tax that could be dedicated to fund development, Sarkozy asked?

Mention of the tax did make it into Gates’s final report, though the paper is more notable for its ideas about how richer emerging markets such as Brazil and China could apply lessons from their recent history to help, for example, boost cassava or rice production in Africa.

But it got him in the door, and for those who typically watch from the sidelines as world leaders gather and depart, it was considered a major step forward.

“It seemed to go well,” Gates said. “The world has achieved a lot in poverty reduction, death reduction, literacy increase, dealing with disease, and we are getting smarter about these things . . . . A lot of times they may think of aid as just a big number. . . . But they can fund research to create new tools and go out and see those tools at work.”