Byline: Matea Gold, Rosalind S. Helderman, Gregory S. Schneider and Frances Stead Sellers

In the fall of 2015, before Stephen Bannon became a trusted adviser to the next president, he launched a daily three-hour radio show that catered to what he called "those 'low-information' citizens who are mocked and ridiculed by their 'betters' - the clueless elites."

Bannon welcomed guests whose views, he often said, had been suppressed by the left's political correctness.

He gave regular airtime to Milo Yiannopoulos, who was banned from Twitter after cheering on supporters who barraged "Ghostbusters" actor Leslie Jones with racist and sexist tweets. Bannon described an anti-Islamic activist who campaigns against what she calls "creeping sharia" in the United States as "a voice in the wilderness." A former Heritage Foundation staffer who had argued that Hispanic immigrants have lower IQs was "one of the smartest brains out there in demographics, demography, this whole issue of immigration," Bannon said.

From his perch as chief of the Breitbart News empire, which produced the satellite radio show, Bannon cemented his role as a champion of the alt-right, an anti-globalism movement that has attracted support from white supremacists and helped power Donald Trump's populist White House victory.

Bannon's appointment as Trump's senior White House counselor is an early sign that the incoming president intends to continue promoting the hard-line approach to issues such as immigration and Islam that galvanized nationalist enthusiasm for his candidacy.

How Bannon rose from provocateur to Oval Office confidant is the story of a man who, like Trump, now rages against the system from which he benefited for years.

As a graduate of Harvard Business School, a former Goldman Sachs investment banker and a Hollywood movie producer, Bannon is in many ways an example of the bicoastal elite that he now disdains.

Although Bannon and those close to him have said he is not racist, he has nonetheless shown a willingness to accommodate "fringe organizations," as he described the extremists attracted to populism in a 2014 address unearthed by BuzzFeed. Eventually, those elements would fall away, he assured the audience: "Over time, it all gets kind of washed out, right?"

Under Bannon's hand, Breitbart articles offered dire warnings of the threats posed by immigrants. Bannon's radio show provided a steady diet of apocalyptic warnings about radical Islam's rise, asserting that Europe had been subject to a "quasi-invasion." Breitbart stories ridiculed feminists, and Bannon himself referred to liberal women as "a bunch of dykes" in a 2011 radio interview. He once angrily denounced a female colleague as a "bimbo" in the 1990s, according to court records. An ex-wife's allegations that Bannon said he did not want his children to attend school with Jews - comments he denied making - have spurred accusations that he is anti-Semitic.

Friends, family and even now-critical former colleagues said the image of Bannon as a bigot is wrong, and miss what really drives the 62-year-old, who was infuriated when people like his father, a longtime phone company worker, saw...