WASHINGTON — Ask Elizabeth Warren, scourge of Wall Street bankers, how they treat consumers, and she will shake her head with indignation. She will talk about morality, about fairness, about what she calls their “let them eat cake” attitude toward taxpayers. If she is riled enough, she might even spit out the Warren version of an expletive.

“Dang gummit, somebody has got to stand up on behalf of middle-class families!” she exclaimed in a recent interview in her office here.

Among all the dramatis personae of post-financial crisis Washington, there is no one remotely like Ms. Warren, 60, who has divided the town between those who admire her and those who roll their eyes at her.

She is an Oklahoma native, a janitor’s daughter, a bankruptcy expert at Harvard Law School and a former Sunday School teacher who cites John Wesley — the co-founder of Methodism and a public health crusader — as an inspiration. She brims with cheer, yet she is such a fearsome interrogator that Bruce Mann, her husband, describes her as a grandmother who can make grown men cry. Back at Harvard, Ms. Warren’s teaching style is “Socratic with a machine gun,” as one former student put it. In Washington, she grills bankers and Treasury officials just as relentlessly.