CHICAGO (CBS) — Former Chicago Teachers’ Union President Karen Lewis has died.

CTU spokeswoman Stephanie Gadlin said, “Our city has lost a great voice.”

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“Karen Lewis was one of the most powerful and prolific voices in public education, advocating for students, their families and the communities in which they live,” Gadlin said. “As her spokeswoman, I cannot tell you how inspired I was by her leadership as well as her vulnerability as she navigated the treacherous terrain of Chicago politics.”

Lewis was not afraid of a fight. In 2012, Lewis led a Chicago teachers strike against Mayor Rahm Emanuel. It was the first Chicago teachers strike in 25 years.

She was elected to head the 30,000-member CTU in 2010. She spent her years in public office working to improve public schools and help teachers while rallying against charter schools.

She became a chemistry teacher after leaving medical school. She taught at three Chicago high schools, including Lane Tech, where she also served on the local school council. That led to her run for CTU president and ultimately talk of challenging Emanuel in the 2015 election.

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At least one poll had Lewis beating Emanuel, but in October 2014 she was diagnosed with an aggressive form of brain cancer. She suffered a stroke in the same area of the brain where she had a tumor removed in 2014.

After months of treatment, she resumed her role as president and secured a third term as contract talks heated up and strike talks resurfaced. At the last hour in October 2016, the second walkout under her leadership was averted.

She continued her public school crusade fighting furloughs and budget cuts.

A stroke in October 2017 sidelined Lewis again. In 2018, Lewis retired as the union’s president. But for many the outspoken, albeit controversial leader had already secured her spot in Chicago history.

Lewis underwent a medical procedure and had been battling health issues for several years.

She spent her years in office working to improve public schools and help teachers, while rallying against charter schools. She taught at three Chicago high schools, including Lane Tech College Prep.

Lewis’ brain cancer diagnosis derailed plans to run against Mayor Emanuel in 2015. She ended up backing Cook County Commissioner Jesus “Chuy” Garcia, who forced Emanuel into a runoff, the first ever in a Chicago mayor’s race.

Emanuel tweeted Monday, “Karen Lewis was a tough and tireless champion for public education and for Chicago’s children, one who was never afraid to fight for what she believed in.

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