Representative Katherine M. Clark of Massachusetts is set to become the House majority leader in January. As a quiet, progressive power player, she will be the first woman to hold this role. "I feel a weight of responsibility," she said. She is known for her skill in managing fellow lawmakers.

A Massachusetts liberal who has never sought the No. 1 leadership spot, Ms. Clark is known as an adept member manager.

Representative Katherine M. Clark of Massachusetts, the No. 2 House Democrat, is set to become the majority leader in January, after her party won control of the chamber.

Ms. Clark, 63, a quiet, progressive power player in Congress, would make history as the first woman to hold that role, though Representative Nancy Pelosi broke a higher glass ceiling in 2007 when she became the first woman to be speaker.

"I feel a weight of responsibility," Ms. Clark said in an interview this week. "It's the women's voices from traveling across my district and the country that really haunt me."

Described by friends as similar in ideology and temperament to Senator Elizabeth Warren, also of Massachusetts, Ms. Clark is set to be the most liberal member on House Democrats' leadership team next year. The majority leader is responsible for setting the schedule, but Ms. Clark has also come to be known in her caucus as a master of member management, keeping up with the needs and issues, both personal and political, of Democratic lawmakers.

Here is what you need to know about Ms. Clark.

She is further to the left on Israel than Hakeem Jeffries.

Speaking at an event in her district last year hosted by a Quaker organization, Ms. Clark described Israel's actions in Gaza as a genocide, when she encouraged people to take action on political issues, including "stopping the starvation and genocide and destruction in Gaza."

That made her the most senior Democrat in leadership to use the term, which she then abruptly retracted. Ms. Clark said in a statement that she had repeated the word "genocide" in response to a question and stated: "I am not accusing Israel of genocide."