蓋茨的資金主要通過全球根除小兒麻痹癥計劃發揮作用，目前這種可怕的疾病已接近根除，全球只有阿富汗和巴基斯坦兩國野外仍有脊髓灰質炎病毒活躍。1988年還有125個國家出現病例。

根除疾病的任務跟基金會幾乎所有項目一樣，運作成熟且由數據驅動。蓋茨資助疾病監控人員經在熱點地區污水系統中抽樣檢查，看是否有潛伏的脊髓灰質炎病毒，然后利用數字衛星數據了解特定地區兒童數量，從而計算接種推廣小組要走訪多少家庭。

基金會還花費超過十億美元，減輕古老且長期被忽視的熱帶疾病（NTDs）造成的負擔，相關疾病可能引發失明、貧血到四肢腫脹等。盡管取得了進展，但仍導致地球七分之一的人口患病。基金會強化了發展中國家的衛生系統，也不斷推動農業創新。（比爾在搞怪又樂觀的蓋茨筆記博客上有一篇博文開頭寫道，“我從不掩飾對化肥的熱情。”）

基金會還在美國發起了全國性關于教育改革的對話，背后有數據支持，也有大量投入的資金支持。（基金會每年花費3億美元用于K-12學習，也在推廣高效學習法。）蓋茨夫婦還改變了家庭慈善事業的性質和規模，2010年與沃倫·巴菲特合作，說服其他億萬富翁在有生之年或在遺囑里捐出至少一半財產。如今已有近200個家庭加入了名副其實的“捐贈誓言”。

“他們每個舉動都會產生乘數效應，”有一次電話采訪中，沃倫·巴菲特如此評價蓋茨夫婦，數十年來巴菲特一直是蓋茨夫婦的好友。后來他向蓋茨基金會捐贈了50萬股伯克希爾·哈撒韋的B股，當時價值約16億美元，從此自己的財富也實現了乘數效應。

“他們每個舉動都會產生乘數效應。兩人行動目標一致。”——沃倫·巴菲特，伯克希爾·哈撒韋董事長兼首席執行官。

但是比爾和梅琳達·蓋茨的影響還不只在金錢方面。巴菲特提到了之前的想法：“他們夫婦倆也有乘數效應，合在一起力量大。兩人的行為目標一致，只是做事風格不一樣，”他說，一邊為自己一針見血指出本質笑起來： “他們直接就來找我，就這么簡單。”

“他們很注重結果，大多數人都不知道如果沒有他們堅持，很多事都不會發生，”U2主唱博諾表示。他和蓋茨夫婦一樣堅持推動全球醫療衛生進步，發起的(RED)基金和ONE運動都獲得了基金會資助。“從我的了解來看，他們對收入的唯一興趣只在于能改變其他人的生活，”他補充說。“他們不求認可，只是不斷堅持做事。就好比，他們搭好攝影棚又找好了攝影師，但太注重結果，有時有忘了讓自己出鏡。”

過去20年里，他們工作幫助改變了數億人的生活。如果現在資助的研究能幫助預防治療艾滋病、耐多藥結核病、瘧疾、被忽視的熱帶疾病和流感，還能多影響數十億人。如果提升婦女權力、提供衛生設施、促進農業和教育（以及提供教育機會）的工作獲得理想的結果，造福世界更是無可估量。

正因如此，《財富》雜志將比爾和梅琳達·蓋茨選入2019年全球最偉大領袖名單。說實話，入選只是一次，但兩人的領導能量絕對是雙倍的。

The Gates money, put to work through the Global Polio Eradication Initiative, has helped bring that horrific paralyzing disease to the brink of elimination, leaving only two places on the earth, Afghanistan and Pakistan, where the wild poliovirus remains active. In 1988, the disease could be found in 125 countries.

The eradication quest is, as nearly all foundation efforts are, sophisticated and data-driven. Gates-funded disease hunters have plumbed sewage systems in hotspot regions to check for lurking poliovirus and used digital satellite data to understand how many kids were in a given area—and, therefore, how many houses inoculation teams needed to visit.

The foundation has spent more than a billion dollars to date to reduce the burden of ancient, and long neglected, tropical diseases (NTDs) that can cause everything from blindness to anemia to an elephantine swelling of limbs—and that, despite the progress made, continue to debilitate one-seventh of the earth’s population. It has fortified health systems in developing countries and brought new innovations to agriculture. (As Bill begins one of his wonkily upbeat GatesNotes blogs, “I’ve never been shy about my passion for fertilizer.”)

The foundation jump-started a national conversation in the U.S. on education reform: one backed by data, as well as dollars—though there have been many of those, too. (It spends $300 million annually on K-12 learning, and on learning about learning.) The Gateses have even changed the nature and scale of family philanthropy—partnering with Warren Buffett in 2010 to convince other billionaires to give half or more of their money away during their lifetime or in their will. Today, nearly 200 families have joined the aptly named “Giving Pledge.”

“Every one of their actions has a multiplier effect,” says Warren Buffett in a phone interview about the pair, with whom he has been close friends for decades. His own fortune became part of that multiplication as well, when he donated 500,000 Berkshire Hathaway B shares to the Gates Foundation—a gift then worth about $1.6 billion.

“Every one of their actions has a multiplier effect. They act with a unity of purpose.” – Warren Buffett, Chairman and CEO, Berkshire Hathaway

But the impact of Bill and Melinda Gates is due to more than money. Buffett returns to his earlier thought: “The two of them have a multiplier effect—the two of them together. They act with a unity of purpose and with a difference of style,” he says, chuckling at the truth of his own line: “That just came to me—and it’s really true.”

“They are so results-orientated that most people have no idea all the things that would not be happening without them,” says Bono, who, like the Gateses, has been a tireless champion for global health, and whose own (RED) and ONE campaigns have received funding from the couple. “For as long as I’ve known them, their only interest in their income is the outcomes it can generate for others in terms of changing lives,” he adds. “They don’t ask for acknowledgment; they just get on with it. They set up the scene, hire the photographer, but are so focused on results, they sometimes forget to be in their own photograph.”

Their work over the past 20 years has helped transform the lives of hundreds of millions of people—and will surely affect billions more if the research they’re funding now helps prevent and cure AIDS, multidrug-resistant TB, malaria, neglected tropical diseases, and the flu. It will help immeasurably more if the work they’re doing now to empower women, provide sanitation, boost agriculture, and improve education (as well access to education) comes to full fruition.

For all that, Fortune has chosen Bill and Melinda Gates as our 2019 World’s Greatest Leader. The pick, pointedly, is a singular one; the power of their leadership is definitely double-barreled.