“Science guy” Bill Nye will join Mona Hanna-Attisha, the doctor who helped expose lead poisoning in Flint, Mich., and Lydia Villa-Komaroff, a molecular biologist who helped develop the technique for making insulin, in headlining the upcoming March for Science in Washington.

Organizers announced on Thursday that the three will be honorary co-chairs and feature in the festivities on the National Mall.

The April 22 event, which will involve the event in Washington and sister events in more than 400 other cities, is shaping up to be one of the scientific community’s biggest demonstrations ever.

Conceived online after President Donald Trump’s inauguration and galvanized by the administration’s handling of science issues, the march has gained a lot of steam in recent months.

In February, some of the nation’s biggest scientific organizations, including the American Association for the Advancement of Science, said they’d join in. Some 800,000 people have said online that they’ll attend one of the events.

Nye said on Wednesday that he’s never seen the scientific community so energized — or troubled by — political issues. Researchers are concerned by the president’s proposed funding cuts to science agencies such as the National Institutes of Health and the Environmental Protection Agency. And everyone should be alarmed by the Trump administration’s skepticism of climate change, Nye said — “the most serious issue facing humankind.”

“Science is what makes our world what it is,” Nye said. “To have a movement or a tendency to set science aside is in no one’s best interest … but nevertheless, that’s what’s happening in the U.S.”

Nye is the only bona fide celebrity of the three co-chairs. The 1990s TV icon, who has squared off against creationists and climate change deniers, is exactly the kind of person you’d expect to headline a science march.

Hanna-Attisha and Villa-Komaroff are giants in the public health and science communities but not necessarily household names.

The Flint pediatrician risked her career to alert officials to the dangerous levels of lead in her patients’ blood. Her whistleblowing drew public attention to the crisis and led to an investigation of the city’s water system.

Time magazine named her one of its 100 most influential people in 2016, and her work garnered awards from environmental and social justice organizations.

In 1975, Villa-Komaroff became the third Mexican-American woman to receive a science doctorate in the United States. Shortly after getting her Ph.D. in the 1970s, she was part of the team of researchers who discovered that bacteria could be used to generate insulin — a vital medication for treating diabetes. She is a fierce advocate for diversity in science and a founder of SACNAS, the Society for Advancement of Chicanos/Hispanics and Native Americans in Science.

These two co-chairwomen were consciously selected to address criticisms that the March for Science hasn’t done enough to include women and minorities, who often face additional barriers working in scientific fields. The organizers — volunteers who are mostly new to political protest — have scrambled to address that and other concerns.

Some people say the march risks turning scientists into an interest group and are skeptical of explicit references to diversity. “Science sees no color” is a frequent refrain in online debates.

On the other hand, many contend that the march needs to be more aggressive in addressing inequality. An early organizer, University of Maine paleoecologist Jacquelyn Gill, quit the march’s steering committee over frustration with its leadership’s handling of diversity issues. The diversity statement on the march website has gone through four revisions as organizers tried to keep up with criticisms.