Updated on 2 January at 4:11 p.m. ET

Right until the end of his life last Wednesday, Ben Barres made it his business to champion the unsung.

While most of his fellow neuroscientists studied neurons, the branching cells that carry electrical signals through the brain, Barres focused his attention on another group of cells called glia. Even though they equal neurons in number, glia were long dismissed as the brain’s support crew—there simply to provide nutrients or structural scaffolding.* But Barres showed that glia are stars in their own right. They help neurons to mature, producing the connections that are the basis for learning and memory, and then pruning those connections so that the most useful ones remain.

In showing how important glia are, Barres revolutionized our understanding of the brain. That alone would have been enough to secure a spot in science’s hall of fame. But the outpouring of adulation that followed his passing, at the age of 63 from pancreatic cancer, was as much about his generosity of spirit as it was about his force of intellect.

Barres was a great scientist, yes, but also a scientist who made it possible for others to be great. He went out of his way to mentor young scientists. He actively stepped out of the way of his trainees so they could blaze their own trails without having to compete with him. And he spent the final days of his life writing and updating dozens of letters of recommendations for his trainees. “He was very sick, but he valiantly worked through these letters and completed every single one of them with utmost care,” says Cagla Eroglu from Duke University. “From the first day in his lab until his death, Ben always cared about my success as if it was his own.”

As news of his death spread through Twitter, his peers called him a “singularity,” a “titan,” and a “moral compass,” who leaves behind a “towering legacy of goodness.” They spoke of unprompted acts of meaningful kindness. “I knocked on his door as a first-year and Ben Barres stayed an hour late to give me advice about women and medicine,” said Natalia Birgisson, a medical student at Stanford University. “I once invited Ben Barres to speak to young LGBT scientists. I sent the email at 11 p.m. and he responded in 10 minutes, agreeing to speak and refusing the honorarium,” said Trevor Sorrells from Rockefeller University. “I interviewed for grad school with Ben Barres and he stopped mid-interview to call another school and advocate on my behalf,” said Alycia Mosley Austin from the University of Rhode Island. As Kay Tye from MIT succinctly said: “Ben Barres was a role model for role models.”

Beyond direct mentorship, Barres repeatedly spoke up for groups who have been historically marginalized in the sciences, including women, minorities, and LGBTQ+ people. He would repeatedly talk about the biases and systemic barriers that keep such groups from succeeding in their careers, often raising the topic in the middle of keynote talks about glia. “Since I have you all trapped on the top of this mountain ... I would like to talk about the many barriers women face in science,” he once told neuroscientists at a conference in Lake Arrowhead.

He most famously talked about those barriers in a searing 2006 opinion piece, published in the prestigious journal Nature. In it, he lambasted several academics for suggesting that “women are not advancing in science because of innate inability,” and spoke of the actual reason for their hindrance: discrimination, both conscious and unconscious.

Barres amassed data and evidence to support his stance, but he also spoke from experience. Born in 1954, he transitioned in 1997 at the age of 43. Before then, as an MIT undergraduate, he solved a hard math problem that had befuddled the rest of his virtually all-male class, only for his professor to suggest that his boyfriend must have done the work. As a Ph.D. student, he lost a fellowship competition to a male peer who had published a sixth as many papers. And as a Stanford professor who had recently transitioned, he heard a faculty member say, “Ben Barres gave a great seminar today, but then his work is much better than his sister’s.”

“By far, the main difference that I have noticed is that people who don’t know I am transgendered treat me with much more respect,” he wrote in Nature. “I can even complete a whole sentence without being interrupted by a man.”

By openly writing about his experiences, Barres made it easier for other female academics to talk about sexism. “As a woman in science, everyone has this feeling that something’s not right, but it’s hard to put that into words in a way that’s compelling to men,” says Carolyn Bertozzi, one of his colleagues at Stanford. “Ben was one of the few people who did the control experiment—what would have happened in a parallel universe where you changed just one variable. [His experiences] were harder for other men to deny.”

As an openly transgender scientist, and the first to be elected to the National Academy of Sciences, Barres also acted as a role model for other trans scientists. “You can’t put a value on it,” says Bertozzi. “The mere existence of Ben Barres—a successful, brilliant, undeniably high-impact scientist who was unashamed and so graceful in demystifying what being transgender means ... he saved lives, I’m sure. Thanks to him, there are countless people who looked in the mirror and said: There’s a place for me in this world.”

Kale Edmiston from the Vanderbilt University Medical Center certainly feels that way. Barres, he told me, took time to meet with him at the biggest annual neuroscience conference, and periodically checked in on him as he finished his Ph.D. “He just radiated encouragement and positivity,” Edmiston said. “At the time we were the only out transgender neuroscientists that we knew of. Trailblazers like Ben made it possible for me to be where I am today.”

Barres blazed similar trails in neuroscience, elevating the long-marginalized glia and forcing other researchers to recognize their value. As a student, he figured out how to isolate and grow them. As a professor, he and his protégés showed that glia govern the life and death of synapses—the connections that transmit signals between individual neurons. Without glia, neurons can’t form mature synapses. And one especially common group of glia, the star-shaped astrocytes, will occasionally devour synapses entirely. Perhaps by keeping the useful synapses and pruning away the useless ones, the glia underlie the brain’s ever-changing nature, and its ability to reshape its circuits to learn from new experiences.

Most recently, Barres’s team, led by postdoc Shane Liddelow, showed that astrocytes can turn fully to the dark side and start killing injured neurons and other glia. These dark astrocytes are more common in degenerative brain diseases like Alzheimer’s, Parkinson’s, multiple sclerosis, and Lou Gehrig’s disease. Barres described that discovery, published while he was undergoing chemo for his cancer, as the most important his lab had ever made. Perhaps glia are behind the destructive symptoms of these conditions. Perhaps they might even point the way to new treatments—the very goal that lured Barres into neuroscience in the first place.

“I’m really not too bothered about dying,” he told Discover magazine in late 2017. “What’s frustrating is that there are so many things I won’t be able to work on. There are so many things I wanted to know.” But scientists contribute to the world not just through their own work, but through the people they train—and Barres knew that better than most. What he didn’t get to personally learn may eventually be discovered by his students, his postdocs, his colleagues, and the people who felt they had a place in science because of his actions.

His trainees see themselves as a family, says Beth Stevens, a former postdoc now at Harvard University. “We will go to bat for each other just as Ben has done so many times for us—a promise we made to Ben that we all intend to keep,” she says. “We will continue to have our annual Barres lab family dinners, traditionally celebrated at the Society for Neuroscience meeting, in his honor for many years to come.”

“Whatever he touched, he left better than when he found it,” adds Bertozzi.

* This piece originally stated that glia outnumber neurons by 10 to 1, and though this is a commonly stated ratio, it’s a myth. The actual ratio is closer to 1:1.