Since leaving the White House, Mr. Davis has built a client list that now includes coup supporters in Honduras, a dictator in Equatorial Guinea, for-profit colleges accused of exploiting students, and a company that dominates the manufacture of additives for infant formula. This month, he agreed to represent the Ivory Coast strongman whose claims to that country's presidency have been condemned by the international community and may even set off a civil war.

Mr. Davis withdrew from his $100,000-a-month contract with Ivory Coast on Wednesday night, saying that the embattled government refused to accept his suggestion to talk to President Obama. Still, his role in West Africa has stoked growing criticism that Mr. Davis has become a kind of front man for the dark side, willing to take on some of the world's least noble companies and causes.

Many lobbying firms have clients with checkered records. Indeed, those are the people who need help the most in Washington. But many activists — and even some government officials — said the list of clients in Mr. Davis's firm stood out.

"You look at who he represents, and the list is just almost unseemly, tawdry," said Meredith McGehee, a lobbyist for California WIC Association, which represents agencies that serve poor women with infant children, and who faced off against Mr. Davis this year in the fight over baby formula, which his client won. "It is an illustration of what most of the American people think of as wrong with Washington."

Mr. Davis says he is aware of the criticism, particularly since his representation of Ivory Coast became an issue. And he is pushing back with some of the same message-molding that earned him a label as a "spinmeister par excellence." He says he's lining up State Department officials, members of Congress and business leaders to testify about how much he has helped them.

Mostly, however, he's single-handedly flooding the zone, writing long, detailed responses to reporters and columnists, and making himself available to anyone interested in directly hearing his side of his story.

"My credibility is the only thing I have," he said in a long, emotional interview on Thursday. "If I defend people in indefensible, corrupt acts, then I lose everything I have, and I'm just another gun for hire. But when I see that I can help get out the facts, and improve people's lives, and peacefully resolve conflicts, then I feel an obligation to do so."

The 65-year-old native of Jersey City said his client list reflected his philosophy that everyone deserved a voice, particularly companies and causes that challenged conventional wisdom or the public's sense of the politically correct. In his career, he has not only embraced controversy, but has also sought it out, portraying himself above all as a crisis manager committed to peacefully resolving conflicts.

That is essentially how Mr. Davis explains his decision to work for the self-declared president of Ivory Coast, Laurent Gbagbo, who has refused to accept that he lost his country's presidential election this month, despite the sanctions and threats of force by his African neighbors.

"I felt great pressure that I could accomplish the avoidance of bloodshed by convincing this man to seek a fair hearing, and to stand down if the result didn't go his way," Mr. Davis said, referring to Mr. Gbagbo. Later, he added, "I thought I could do some good."

He similarly explained his work as one of three foreign agents for the government of Equatorial Guinea, which has been governed for three decades by Teodoro Obiang Nguema Mbasogo. Rights groups and anticorruption activists have accused Mr. Obiang of embezzling hundreds of millions of dollars from his tiny oil-rich West African state, while most of its people scrape by in dire poverty.

"I'm a liberal Democrat," Mr. Davis said, referring to his work for Mr. Obiang. "I've been a liberal Democrat all my life. I haven't changed my values. But what am I supposed to do if the leader of a country comes to me and says he wants to get right with the world, and get right with the United States? Am I supposed to say no, and let him go on doing what he's doing? Or should I try to help him get right?"

Obama administration officials say Mr. Davis is on the wrong side of some of these fights.

Helene Cooper contributed reporting.