8 June 1938 - 18 August 2018 The philanthropist remembers the Nobel peace prize winner and UN secretary general who she worked with in the fight against global poverty • Stephen Hawking remembered by Bernard Carr • Read the Observer’s obituaries of 2018 in full

It was 2012, and somewhere on a cassava and banana farm in rural Tanzania, there were four of us standing in a circle: me, two farmers named Joyce and Elijah, and the former secretary general of the United Nations, Kofi Annan.

Elijah and Joyce did most of the talking. They told us how this farm was unlike any they had worked on; how there were improved crop varieties and new tools to process the harvest. There was even a daycare centre near the farm. This way, women could spend more time selling what they grew. I rattled off some questions. Do you sell your cassava only here – or do you ship it somewhere else? How far is the market? Have you seen a difference in your yields? Kofi, though, mostly listened.

Later, after we left the fields and walked towards the daycare centre where there was a bigger crowd, Kofi started talking. He was telling jokes, trying to put everyone at ease, and doing a very good job of it. The man had the deepest, most infectious laugh I’ve ever heard and an incredibly commanding voice. He sounded like an actor playing himself. (In fact, he once told me about the time he’d been mistaken for Morgan Freeman.)

Kofi and I had attended a lot of the same UN events, and he’d visited our foundation’s offices in Seattle a few times, so I’d seen him charm a room before. But this day on the cassava farm was different. He was utterly at home here. I suppose I shouldn’t have been surprised: Kofi Annan, of all the world leaders I had met, had spent the most time thinking about how to help places like this farm and people like Joyce and Elijah.

Facebook Twitter Pinterest Kofi Annan comforts a crying baby as he meets survivors of the Liquica massacre in East Timor, 1999. Photograph: Ed Wray/AP

When my husband Bill and I started our foundation in 2000, we still had so many questions about the best ways to fight poverty and disease, and Kofi, it seemed, already had the answers. That year, he’d written a manifesto about the UN’s role in the 21st century. In its final pages, he’d included a set of targets around poverty and disease reduction that he wanted the world to achieve by 2015. These became known as the Millennium Development Goals, and at first, critics dismissed them outright. Cut extreme poverty in half? Halt the spread of HIV, malaria and TB, the three greatest killers in poor countries? At best, it was overly optimistic.

Kofi wasn’t satisfied with just setting the goals, though. He wanted to push the world to achieve them. No other secretary general was so able to connect the UN’s heart with its brain, its mission to lift up the sick and the poor with an effective plan for doing so. He was a master, too, at bringing world leaders along for the ride.

Today, there are 27 million people alive who would have otherwise died from HIV-related illness, TB or malaria. And they live, in large part, because Kofi rallied the world to establish the Global Fund, which pays for medicines – and things that prevent those diseases from spreading, such as mosquito nets. The world met its goal of halving the global poverty rate by 2015; in fact, it did so five years ahead of schedule, in 2010. “Development experts,” one observer wrote, “are still rubbing their eyes.”

Play Video 1:04 Kofi Annan's three key UN speeches - video

When he received the Nobel peace prize in 2001, Kofi said that “today’s real borders are not between nations, but between the powerful and powerless”. He saw Africa’s small farmers as part of the latter camp and wanted to give them a way to lift themselves out of poverty. This was what led us to that cassava farm back in 2012.

I remember that after our visit that day, Kofi thanked me for the foundation’s work. He was generous in his praise, and then he gave me a nickname. “Mama Melinda,” he called me.

It was a term of respect, typically given to an elder, and I was flattered but taken aback. Mama Melinda? If there was one person who deserved such an honour, I thought, it wasn’t me.

Kofi Annan was a true founding father of modern global development.