WASHINGTON (Reuters) - Three congressional committees and the Department of Justice are investigating the Internal Revenue Service‘s scrutiny of conservative groups seeking tax-exempt status as the scandal distracts from President Barack Obama‘s second-term agenda.

Below are some of the major players in the backlash over the IRS paying extra attention to advocacy groups whose names included terms such as “patriot” or “Tea Party” when considering applications for tax-exempt status.

* Steven Miller - The acting head of the Internal Revenue Service while the scandal unfolded. He was fired from the post on Wednesday after an internal IRS report found that poor management, and not partisan politics, led to an “inappropriate” focus on conservative groups starting in 2010. The IRS has acknowledged Miller knew about the targeting of conservative groups in 2012 but did not disclose the practice. He was the former deputy IRS commissioner for services and enforcement and had been at the agency for more than 25 years.

At a House of Representatives hearing on Friday, Miller apologized for “foolish mistakes” made at the IRS and said they resulted from a heavy workload. He leaves the agency in June.

* Douglas Shulman - IRS commissioner before Miller took over in the acting capacity in November 2012. A Democrat, he was appointed to the post under Republican President George W. Bush in 2008.

In March 2012, Shulman told lawmakers that IRS personnel applied no extra scrutiny to conservative groups, although the new report from the Treasury Inspector General for Tax Administration (TIGTA) said that Miller knew of the targeting as early as March 8, 2012.

Congressional leaders sent letters to Shulman inquiring about IRS targeting as early as June 2011. According to the inspector general, the IRS’s Determinations Unit began targeting conservative groups in March or April of 2010.

* Danny Werfel - the White House budget official selected by Obama to replace Miller as acting IRS chief on May 22.

The Obama administration‘s point man in overseeing the “sequestration” budget cuts, he will now tackle the IRS scandal.

* Lois Lerner - director of the IRS’s tax-exempt division who broke the news of the scandal on May 10 at an American Bar Association function when she publicly apologized for the discriminatory practices. The admission came just days after she testified in Congress but did not mention it. According to the inspector general, Lerner learned about the targeting as early as June 29, 2011.

Lawmakers have called for her removal from the IRS.

Miller on Friday acknowledged that the scandal-exposing question-and-answer session had been planned.

* Joseph Grant - IRS acting commissioner of tax exempt/government entities division at the center of the scandal. On Thursday he announced plans to retire on June 3 after joining the IRS in 2005. He took over the reins of the tax exempt division in late 2010 and Lerner worked under him.

* Sarah Hall Ingram - Preceded Grant as head of the IRS’s tax-exempt division when the targeting of conservative groups began. Since December 2010, she has headed up the IRS division handling Obama administration’s healthcare reform.

* William Wilkins - IRS chief counsel who is an Obama political appointee. He is the top legal adviser and takes the lead on all litigation involving the IRS. His office, although not necessarily Wilkins personally, knew of the targeting as early as August 2011, according to TIGTA. The IRS said Wilkins did not participate in the August 2011 meeting, which the agency said involved “staff attorneys several layers below Wilkins.”

* J. Russell George - Treasury Department inspector general for tax administration. Investigated the complaints against the IRS and issued the public report on targeting of conservative groups. The IRS is an arm of the Treasury Department and lawmakers at the hearings are scrutinizing George for not issuing warnings about the practice earlier.

* IRS’s Cincinnati field office employees - oversaw the reviews of tax-exempt applications. According to TIGTA, the Ohio unit set its own criteria for checking tax-exempt groups in the absence of clear guidance from more senior officials.

Republican lawmakers have named five workers they hope to bring in for questioning: Holly Paz, Washington-based director of rulings and agreements for the tax exempt division; Greg Muthert, a veteran Cincinnati office worker; Joseph Herr and Elizabeth Hofacre, who were cited by some Tea Party groups as handling their tax-exempt applications; and John Shafer, whom lawmakers described as “screening group manager.”

A congressional aide said the five workers were chosen based on a timeline from the TIGTA report that listed the job roles involved in the activity. It was unclear whether these employees had any role in any wrongdoing.

* President Barack Obama - has said he was not aware of the ongoing practice, calling it intolerable and inexcusable. His Press Secretary Jay Carney said the White House Counsel was notified of the IRS’s targeting during the week of April 22.

Obama has appeared multiple times in public to condemn the IRS’s actions and has promised to cooperate with congressional investigations and a Justice Department probe, but he has not demanded a special prosecutor look into the allegations.

* Representative Dave Camp - Republican chairman of the House Ways and Means Committee that is investigating the matter. On June 3, 2011, he sent a letter to then-Commissioner Shulman, inquiring about IRS targeting of taxpayers who donated to conservative groups and audits of tax-exempt organizations. The IRS then halted reviews of any tax-exempt groups but never addressed targeting concerns.

* Representative Darrell Issa - Republican chairman of the Oversight and Government Reform Committee also conducting an investigation. He is seeking interviews with five IRS employees to learn more about the tax-exempt reviews.

* Senator Max Baucus - Democratic chairman of the Senate Finance Committee, who said his tax code revamp will examine rules for nonprofit group’s political activities in hopes of preventing such scandals in the future.

(Reporting by Alina Selyukh; editing by Jackie Frank)