Eric Holder, who made history as the first African American to lead the Justice Department, announced his resignation as attorney general Thursday. President Obama praised Holder thanking him for his service and dedication to justice for all Americans. (AP)

Eric H. Holder Jr., who made history as the nation’s first African American attorney general and became an icon among liberals but a divisive figure to many conservatives, announced Thursday that he will resign his post.

In an emotional ceremony at the White House, President Obama paid tribute to one of the last original members of his Cabinet and a close friend, calling Holder’s departure “bittersweet.” Holder, at one point fighting back tears, cited a series of actions he said his Justice Department took to empower the powerless, ranging from fighting for voting rights to reforming criminal sentences for low-level drug offenders.

“I have loved the Department of Justice ever since, as a young boy, I watched Robert Kennedy prove during the civil rights movement how the department can — and must — always be a force for that which is right,’’ said Holder, who plans to remain in office until his successor is confirmed.

The nation’s fourth-longest-serving attorney general, Holder leaves a complicated legacy, one in which the very qualities that have endeared him to liberals — such as his pursuit of legal equality for gay men and lesbians and his focus on strengthening civil rights protections — have often left him at odds with Obama’s opponents. He tried to revitalize the Justice Department’s Civil Rights Division and spoke with unusual candor about racial matters, becoming the chief surrogate on race for an African American president who felt less comfortable tackling the sensitive issue in public.

The wildly disparate reactions to Holder’s departure on Thursday captured the complex nature of his tenure. Throughout the day, praise for Holder poured in from Democrats, civil rights leaders and others. They called him an influential proponent of civil liberties and sentencing and drug law reforms who also helped protect Americans from terrorist attacks. “His resignation is a great loss for any American seeking justice in our society,” said Rep. John Lewis (D-Ga.), a revered figure of the civil rights movement who spoke to Holder on Thursday before news of his resignation became public.

Attorney General Eric Holder is resigning from his post as the longest-serving member of President Obama’s Cabinet. From the “Fast and Furious” scandal to collecting reporters’ phone records to the Defense of Marriage Act, here’s a look at Holder’s comments on some of the biggest controversies during his nearly six-year tenure at the Department of Justice. (Jackie Kucinich, Julie Percha/The Washington Post)

But Holder’s pending departure — while not unexpected, since he had considered leaving several times before — immediately reignited the partisan battles over his legacy that marked much of his nearly six-year tenure. Even as the attorney general privately informed top Justice Department staff members Thursday of his plans to leave, Republicans blasted him as a liberal activist focused more on pursuing his own agenda than enforcing the law.

“Eric Holder is the most divisive U.S. Attorney General in modern history,’’ Rep. Darrell Issa (R-Calif.), chairman of the House Oversight and Government Reform Committee, said in a statement. “By needlessly injecting politics into law enforcement, Attorney General Holder’s legacy has eroded more confidence in our legal system than any Attorney General before him.’’

A Nevada congressman, Mark Amodei, more succinctly captured the feeling of many Republicans about Holder’s exit. “Thank you,’’ he said in a two-word statement.

It was Issa, however, who was behind perhaps the most ignominious moment in Holder’s tenure, when the House voted in 2012 to hold him in contempt of Congress over his handling of the department’s controversial “Fast and Furious” operation, a botched anti-weapon-smuggling investigation. Holder and other Democrats vehemently opposed the move, calling it partisan politics.

Although the White House has begun interviewing candidates to replace Holder, people familiar with the search said there may be no nominee until after the November midterm elections. Among the possible candidates, those people said, are Solicitor General Donald B. Verrilli Jr.; Jenny Durkan, who is stepping down as U.S. attorney in Seattle next week; Tony West, who recently stepped down as associate attorney general; former White House counsel Kathryn Ruemmler; Loretta E. Lynch, the U.S. attorney in Brooklyn; and Preet Bharara, the U.S. attorney in Manhattan.

When Holder — who has clashed with Republicans on other issues such as voting rights in a number of searing congressional hearings — would leave office has been has been fodder for intense speculation in Washington.

People familiar with the attorney general’s thinking said he has found the job exhausting at times and considered leaving last summer and fall in the heat of the Fast and Furious controversy. But Holder was reluctant to exit at a low point and wanted to do so on his own terms.

Since then, he has announced prison- and sentencing-reform initiatives and reengaged on the issue of racial justice in light of the shooting of an unarmed black teenager in Ferguson, Mo.

Another factor in Holder’s departure, said people who have spoken with him, emerged when he was taken to a Washington hospital in February after a health scare involving lightheadedness and shortness of breath. The incident, the people said, made Holder reevaluate his life and his priorities going forward.

Holder discussed his plans with Obama on several occasions in recent months, according to a Justice Department official, and finalized those plans in an hour-long conversation with the president at the White House residence over Labor Day weekend.

Though a close confidant of Obama’s, Holder has had a tense relation with others in the White House. During the president’s first term, the attorney general clashed frequently with some White House aides who came to view him as politically tone-deaf. Just a few weeks after the inauguration of Obama, the nation’s first African American president, for example, the attorney general stirred up ire among conservatives by saying that on racial matters, America has “always been and continues to be, in too many ways, essentially a nation of cowards.’’

Later, Rahm Emanuel, then Obama’s chief of staff, fought Holder on his highly public announcement that he hoped to try terrorism suspects in federal courts, part of his legal team’s work to help close a U.S. military prison at Guantanamo Bay, Cuba., and deliver on an early campaign promise of Obama’s.

In one infamous incident, Holder and Emanuel reportedly cursed each other when Emanuel said the politics of Holder’s Guantanamo plans were threatening to undercut White House efforts to reform health care. The attorney general was forced to reverse course, canceling plans to hold major terrorism trials in a Manhattan federal court instead of at Guantanamo.

But Holder now exits after a series of successes in the past year, having received accolades from community activists for his leadership in investigating and responding to the police shooting of an unarmed teenager in Ferguson. Holder has often spoken about race relations in blunter terms than the president, and to this day tells friends and colleagues that he stands by his “nation of cowards” remark and thinks it led to a vital national debate about racial justice.

At a speech this week at New York University’s Brennan Center for Justice, Holder said the Ferguson shooting and subsequent protests have left the country at a “moment of decision” about how police interact with racial minorities.

The attorney general also proudly noted that the federal prison population has dropped by nearly 5,000 inmates this year, the first decline in decades.

While Holder has no immediate plans after he leaves office, a Justice Department official said, he has spoken with friends and colleagues about establishing a center to continue his work on restoring trust between law enforcement and minority communities.

Carol D. Leonnig, Hamil R. Harris, Ed O’Keefe and Peyton Craighill contributed to this report.