A House select committee has been formed to scrutinize the causes of the Jan. 6 riot at the U.S. Capitol. The riot occurred as Congress met to formalize Joseph R. Biden Jr.’s election victory amid efforts by President Donald J. Trump and his allies to overturn the results.

Here are some of the key people and groups included so far in the panel’s investigation:

Trump, His Family and His Inner Circle

Donald J. Trump

The former president’s White House records related to the attack have been a focus of the inquiry. Mr. Trump unsuccessfully tried to keep these documents from the committee by claiming executive privilege. The panel is also scrutinizing Mr. Trump’s role in proposals to seize voting machines after the 2020 election.

Ivanka Trump

The daughter of the former president, who served as one of his senior advisers, has been asked to cooperate. The panel said that it had gathered evidence that she had implored her father to call off the violence that occurred when his supporters stormed the Capitol.

Rudolph W. Giuliani

Mr. Trump’s personal lawyer and three members of his legal team — Jenna Ellis, Sidney Powell and Boris Epshteyn — pursued conspiracy-filled lawsuits that made claims of voter fraud and played central roles in the effort to use courts, state legislatures and Congress to overturn the results.

Stephen K. Bannon

The former Trump aide is under scrutiny by the committee for comments he made on his radio show on Jan. 5, 2021. The committee points to this as evidence that he had “some foreknowledge” of the attack. Mr. Bannon has been charged with contempt of Congress for refusing to comply with a subpoena; he claimed protection under executive privilege even though he was an outside adviser.

Michael T. Flynn

Mr. Trump’s former national security adviser attended an Oval Office meeting on Dec. 18, 2020, in which participants discussed seizing voting machines and invoking certain national security emergency powers. Mr. Flynn has filed a lawsuit to block the panel’s subpoenas.

White House Officials

Mark Meadows

Mr. Trump’s chief of staff, who initially provided the panel with a trove of documents that showed the extent of his role in the efforts to overturn the election, is now refusing to cooperate. The House voted to recommend holding Mr. Meadows in criminal contempt of Congress for defying the panel’s subpoena.

Mike Pence

The former vice president could be a key witness as the committee focuses on Mr. Trump’s responsibility for the riot and considers criminal referrals, but Mr. Pence has not decided whether to cooperate, according to people briefed on his discussions with the panel.

Marc Short

Mr. Pence’s chief of staff, who has firsthand knowledge of Mr. Trump’s pressure campaign on the vice president to throw out the election results, testified before the panel under subpoena. He is the most senior person on Mr. Pence’s staff who is known to have cooperated with the committee.

Members of Congress

Kevin McCarthy

The panel has requested an interview with Mr. McCarthy, the House Republican leader, about his contact with Mr. Trump during the riot. A California representative who could become speaker of the House after the midterms in November, Mr. McCarthy has refused to cooperate.

Scott Perry and Jim Jordan

The representatives from Pennsylvania and Ohio are among a group of Republican congressmen who were deeply involved in efforts to overturn the election. Both Mr. Perry and Mr. Jordan have refused to cooperate with the panel.

Outside Advisers and Groups

Roger J. Stone Jr.

The longtime political operative, who promoted his attendance at rallies on Jan. 5 and 6 and solicited support to pay for his security, has become a focus of the panel as it digs further into the planning and financing of rallies before the attack.

Phil Waldron

The retired Army colonel has been under scrutiny since Mr. Meadows turned over a 38-page PowerPoint document that Mr. Waldron had circulated on Capitol Hill. The document contained plans that detailed how to overturn the election.

Jeffrey Clark

The Justice Department official repeatedly pushed his colleagues to help Mr. Trump undo his loss. The panel has recommended that Mr. Clark be held in criminal contempt of Congress for refusing to cooperate with a subpoena.

John Eastman

The little-known academic and conservative lawyer has become the subject of intense scrutiny since writing a memo that laid out how Mr. Trump could stay in power.

Fake Trump electors

Fourteen people falsely claimed to be electors for Mr. Trump in the 2020 election in states that Mr. Biden had won: Arizona, Georgia, Michigan, New Mexico, Nevada, Pennsylvania and Wisconsin.

Far-Right Figures

Extremist groups

The panel is scrutinizing some white nationalist leaders and militia groups, including the Proud Boys and the Oath Keepers. It is intensifying its focus on the rallies that led up to the mob violence and how extremists worked with pro-Trump forces to undermine the election.

Alex Jones

The conspiracy theorist helped organize the rally that occurred before the riot, and said that White House officials told him that he was to lead a march to the Capitol, where Mr. Trump would speak, according to the committee.

Media Entities

Fox News anchors

Sean Hannity sent text messages to Trump officials in the days surrounding the riot that illustrate his unusually elevated role as an outside adviser. Mr. Hannity, along with Laura Ingraham and Brian Kilmeade, also texted Mr. Meadows as the riot unfolded.

Big Tech firms

The committee has criticized Alphabet, Meta, Reddit and Twitter for allowing extremism to spread on their platforms. The panel has said that the four social media companies have failed to adequately cooperate with the inquiry.

And a Key Event

Willard Hotel meeting

Several Trump advisers and allies — including Mr. Giuliani, Mr. Bannon, Mr. Flynn, Mr. Stone, Mr. Jones and Mr. Eastman — gathered at the Willard Hotel near the White House the day before the riot. The events that unfolded there have become a prime focus of the committee.