The greatest scientists are remembered not only for their discoveries but for their characters. To make the biggest imaginative leaps you need not just intellect but a particular set of values: courage, honesty, a certain rebelliousness, and ceaseless curiosity. In individuals as different as Galileo, Darwin and Einstein, these values were present.

Stephen Hawking, who passed away on March 14, exemplified this pattern. His work distinguished him as one of the greatest physicists of our generation. His character distinguished him as one of its greatest men.

I first met Professor Hawking in 1987, when he attended a physics conference in Moscow. There was excitement in the air. For us younger physicists, he was already a revered figure. His work on black holes had built an elegant bridge between quantum theory and general relativity. And it had shocking implications: that black holes are not completely black—they emit radiation (now called “Hawking radiation”)—and that any information falling into a black hole is scrambled and lost forever.

This may not seem like a big deal—if you were careless enough to drop this article in a black hole, would you expect it to remain readable? But to physicists it was deeply unsettling. The laws of nature depend on events being predictable, in principle, from their pasts. If black holes are “wells of forgetfulness,” as Hawking put it recently, in which the past is lost for good, can nature be said to have laws at all? “It’s like the universe losing its cell phone,” Hawking said. “Worse than that—losing its memory.”

Back at that Moscow conference, we were all aware that he had achieved these insights in spite of his debilitating illness. But it was one thing to hear about him, another to see him in person. Although I eventually quit physics—we can’t all be as good as Stephen Hawking, after all—he made a deep and permanent impression on me that day. His words were mediated by his interpreter, but the quality of the man came through loud and clear. Here was both a great mind and one that absolutely embodied those scientific values of courage, honesty, curiosity and rebelliousness. (This last one, I suspect, played a big part in enabling him to outlive his prognosis by 55 years.)

These values often took him well beyond the bounds of academia. They led him to speak out about culture, politics and existential risks facing humanity. He was just as committed to the public understanding of science as he was to science itself, whether it was via popular books, lectures or TV shows. Indeed, he reportedly turned down a knighthood as a protest against insufficient funding for science.

Happily, in 2013 he did agree to accept the Breakthrough Prize, which I had founded a year earlier, in part to raise awareness of the funding issue and the significance of fundamental science. The prize recognized his immense influence on the course of modern physics. In the last two decades, the issues he raised about black holes and information have become perhaps the most fertile area of physics, where many expect the next big breakthrough to emerge. The famous string theorist Leonard Susskind wrote of this work, “I believe that in time, when the repercussions are fully understood, physicists will recognize it as the beginning of a great scientific revolution.”

In recent years, I had the good fortune to spend more time with Professor Hawking when he partnered with me to launch two science initiatives: Breakthrough Listen, a new astronomical search for evidence of intelligent life beyond Earth; and Breakthrough Starshot, the first practical attempt to design a space probe that could travel to another star. By now in his mid-seventies, his curiosity was still as fierce as ever. He supported these projects because he was burning to know whether we are alone in the universe, and whether humanity can survive our current challenges and reach out for the stars.

Unusually for a physicist, he was also still producing important science. In 2016 he and his collaborators published a major new paper on black holes and information. By then, with characteristic honesty and intellectual courage, he had decided that he had drawn the wrong conclusion from his early work. He was now convinced that information survives—that the universe does not forget.

One thing is certain: for as long as there is science, the legacy of Stephen Hawking, the scientist and the man, will be remembered.