Neuroscientist Ben Barres, who made groundbreaking discoveries in the role certain cells play in the brain, died on December 27 at age 63. The chair of the neurobiology department of Stanford University, Barres had been fighting pancreatic cancer for more than a year.

He is best known for establishing the importance of glial cells, which comprise 90% of brain cells but had been previously dismissed as unimportant.

But Barres was also a staunch advocate for trans rights and never hesitated to attack bad science about gender identity. He was the first trans person admitted into the National Academies of Science.

“Ben was a remarkable person. He will be remembered as a brilliant scientist who transformed our understanding of glial cells and as a tireless advocate who promoted equity and diversity at every turn,” said Stanford president Marc Tessier-Lavigne in a statement. "He was also a beloved mentor to students and trainees, a dear friend to many in our community and a champion for the fundamental dignity of us all.”

An August article in Discover explains the importance of Barres’ discovery:

Glia were long regarded mainly as a maintenance crew, performing such unglamorous tasks as ferrying nutrients and mopping up waste, and occasionally mounting a defense when the brain faced injury or infection. Over the past two decades, however, Barres’ research has revealed that they actually play central roles in sculpting the developing brain, and in guiding neurons’ behavior at every stage of life.

“He has made one shocking, revolutionary discovery after another,” says biologist Martin Raff, emeritus professor at University College London, whose own work helped pave the way for those advances.

The Alzheimer's Drug Discovery Foundation praised Barres’ work and dedication: "The pipeline of drugs in development for Alzheimer’s owes so much to Ben Barres. He was a visionary scientist and generous mentor."

He took leave from his duties in April 2016 when he was diagnosed.

"The thing about having a terminal disease is, everybody knows they're going to die at some point," he said in a recent YouTube video. "But the hardest part is this incredible time I've been having in science just comes to an end. There's all these questions I'm curious about. And I [was] hiring new students and post-docs when I got sick, and I just told them all not to come."

Transitioning in his 40s, Barres was acutely aware of the institutional prejudice faced by women in academia, especially in STEM fields.

“Until intolerance is addressed, women will continue to advance only slowly,” Barres once wrote in a 2006 essay in Nature. “The comments … about women’s lesser innate abilities are all wrongful and personal attacks on my character and capabilities, as well as on my colleagues’ and students’ abilities and self-esteem. I will certainly not sit around silently and endure them.”