WASHINGTON - 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 for many conservatives, announced Thursday that he would 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 with a complicated legacy, one in which the very qualities that have endeared him to liberals - such as his pursuit of legal equality for gays 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 Thursday captured the complex nature of his tenure. Praise poured in from Democrats, civil rights leaders, and others, who 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.

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 Thursday of his plan 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 "Fast and Furious" operation, a botched weapons-smuggling investigation.

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" battle. But Holder was reluctant to exit at a low point and wanted to do so on his own terms.

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.

Eric H. Holder Jr.

Age: 63; born Jan. 12, 1951, in New York.

Experience: Sworn in as the 82d attorney general of the United States on Feb. 3, 2009. Previously, he was litigation partner at Covington & Burling L.L.P. in Washington. Appointed deputy attorney general in 1997. Before that, he served as U.S. attorney for the District of Columbia.

Education: American history graduate of Columbia College, 1973. Columbia Law School, 1976.