Age: 49
Occupation: Administrator of the U.S. Environmental Protection Agency
Previous TIME 100 appearances: 1
Trained as a chemical engineer, Lisa Jackson spent 16 years with the Environmental Protection Agency (EPA) before becoming head of the New Jersey Department of Environmental Protection and later chief of staff to then New Jersey governor Jon Corzine. She returned to the EPA under President Obama, becoming the first African American to head the agency. Her steadfast push for action on climate change and air pollution has earned her the enmity of the GOP, and she'll be called to testify early and often on Capitol Hill. Whatever one might think of the policies she pursues, few doubt that she'll face the congressional grillings with grace.