Ellen Tauscher, a former Democratic congresswoman from California who also served in a key State Department post during the Obama administration, has died at the age of 67.

In her role as Undersecretary of State for Arms Control and International Security Affairs, Tauscher negotiated arms treaties for the U.S. She was also one of the first women with a seat on the New York Stock Exchange at age 25. Later, she was an officer of the American Stock Exchange.

Tauscher's family said in a statement Tuesday that she died of pneumonia and that she was surrounded by family at the time of her death.

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"Ellen was a force to be reckoned with from the time she was a young girl growing up in Harrison, New Jersey," the family said. "She succeeded at everything she did and made her mark wherever she went. She was the strongest, bravest person we have ever known."

Former Secretary of State Hillary Clinton Hillary Diane Rodham ClintonDemocratic groups using Bloomberg money to launch M in Spanish language ads in Florida The Hill's Campaign Report: Presidential polls tighten weeks out from Election Day More than 50 Latino faith leaders endorse Biden MORE, who worked with Tauscher, called her "fearless, brilliant, and bighearted" in a statement, adding that Tauscher's "outstanding service and kind, good soul made the world better for everyone around her."

Clinton told Politico that Tauscher was "the most important person in getting us to the negotiation of the New START Treaty," which limits the number of nuclear warheads Russia and the U.S. can deploy.

"In my opinion, it would not have happened without her," Clinton said.

Bill and I are deeply saddened by the passing of our dear friend Ellen Tauscher. Ellen woke up every day determined to make a difference, and make a difference she did. pic.twitter.com/86BRmtB4Qt — Hillary Clinton (@HillaryClinton) April 30, 2019

Tauscher also chaired Sen. Dianne Feinstein Dianne Emiel FeinsteinFeinstein 'surprised and taken aback' by suggestion she's not up for Supreme Court fight Democrats shoot down talk of expanding Supreme Court Biden leads Trump by 12 points among Catholic voters: poll MORE's (D-Calif.) first two Senate campaigns. The senator said in a statement that her former campaign leader "had a huge heart and was always ready with a story."

“When Ellen put her mind to politics, she was a force,” Feinstein added.

The passing of Ellen Tauscher is a loss for us all. Ellen was brilliant, gracious and generous and always did her level best to lift up those around her. She’ll always be remembered. pic.twitter.com/cfai1mmGe3 — Sen Dianne Feinstein (@SenFeinstein) April 30, 2019

Adam Parkhomenko, who worked with Tauscher on the Ready for Hillary Super PAC, described the former California congresswoman as an intelligent and positive person who was a mentor to many.

"When she was helping them along in their careers and giving them advice, she didn't look at them as if they were beneath her," he said in an interview. "She really treated everybody, no matter who they were, as her equal."

House Speaker Nancy Pelosi Nancy PelosiHoyer: House should vote on COVID-19 aid — with or without a bipartisan deal Ruth Bader Ginsburg lies in repose at Supreme Court McCarthy threatens motion to oust Pelosi if she moves forward with impeachment MORE (D-Calif.) commended Tauscher's commitment to nonproliferation in a statement.

"To watch Ellen wield the gavel was to observe a masterclass in steady, steely leadership," she said. "Her relentless commitment to nuclear nonproliferation, which is a pillar of America’s national security, beautifully honored the oath we all take: to support and defend the Constitution, and protect the American people."

Updated: 1:55 p.m.