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The Earth avenger doesn't just see green as the Hulk: He founded the clean water organization Water Defense in 2010 and has been unafraid to criticize politicians on both sides of the aisle for warmongering, economic inequity, and inaction on what he sees is one of the most dire threats to our environment—hydraulic fracturing, or frakking, the process of drilling into rock with pressurized liquid to extract natural gas.
"The good news is we don't need superhero strength to protect our planet," Ruffalo wrote in an essay for Grist.org in 2015. "We need education, and a collective, grassroots movement that is well underway. As students across the country walk across graduation stages, wrestling with what comes next, I want to remind all of them of the power they have and the responsibility they bear."
His 2019 film Dark Waters, in which he played real-life lawyer Rob Bilott, the corporate attorney who switched sides and took on DuPont after learning that chemical run-off was poisoning a farmer's livestock, was a years-on-the-making passion project for Ruffalo. He and Bilott met last year with members of Congress from both sides of the aisle to talk about ending the U.S. military's use of "forever chemicals" that end up in our water supply—and inevitably in animals and people.