Steve Bannon, 62, landed the White House position on Sunday while outgoing Republican National Committee chairman Reince Priebus was appointed chief of staff. Bannon had also been viewed as a candidate for the position.
Bannon, who emerged as the leader of the alt-right during the last months of Trump's campaign, is an anti-establishment counterpart to GOP figure Priebus.
But Bannon's lack of gusto for the ruling class hasn't kept him from knocking on the door of two of the world's most exclusive clubs: Wall Street and Hollywood.
Bannon, who is of Irish Catholic descent, graduated from Georgetown University with a master's degree in national security studies and went to Harvard Business School hoping to land a Wall Street job.
He matriculated in 1983, became a US Navy officer, then joined Goldman Sachs as an investment banker.
His Wall Street stint was followed by a Hollywood career, during which Bannon worked as the executive producer of Sean Penn's 1991 drama 'The Indian Runner'.
Bannon became an executive producer in Hollywood and secured part of the shares from TV show 'Seinfeld' in 1993.
In the 1990s, Bannon's then-wife Mary-Louise Piccard accused him of grabbing her 'by the throat and arm' and of threatening her, according to documents previously obtained by the New York Post.
Piccard later said in court documents filed in 2007 that he didn't want his daughters 'going to school with Jews'.
The early 2000s saw Bannon working on more documentaries. He wrote, co-produced and directed his own film in 2004, 'In The Face Of Evil: Reagan's War In Word And Deed'.
Bannon has credited Reagan with spurring his own political views.
'I come from a blue-collar, Irish Catholic, pro-Kennedy, pro-union family of Democrats,' Bannon told Bloomberg last year.
'I wasn't political until I got into the service and saw how badly Jimmy Carter f****d things up. I became a huge Reagan admirer. Still am. But what turned me against the whole establishment was coming back from running companies in Asia in 2008 and seeing that Bush had f****d up as badly as Carter. The whole country was a disaster.'
The documentary is thought to have led to Bannon's meeting with Andrew Breitbart, the founder of the eponymous right-wing website.
Bannon took over as executive chairman of Breitbart News following Breitbart's death in 2012 and stayed there for four years, until the Trump campaign recruited him in August.
'We call ourselves 'the Fight Club'. You don't come to us for warm and fuzzy,' Bannon once told the Washington Post about the website.
'We think of ourselves as virulently anti-establishment, particularly 'anti-' the permanent political class. We say Paul Ryan was grown in a petri dish at the Heritage Foundation.'
Bannon in 2012 also became the chairman of the Government Accountability Institute, an investigative research organization that published the anti-Clinton book 'Clinton Cash' and also went after Jeb Bush with 'Bush Bucks'.
The Trump campaign recruited Bannon in August this year, while Kellyanne Conway became campaign manager.
Bannon previously made no secret of his disdain for GOP leaders. He once wrote in an email, according to the Daily Beast: 'Leadership are all c***s. We should just go buck wild.'
The remark, the Daily Beast wrote, came after Bannon learned that Breitbart hadn't been invited to a meeting held by Representative Jason Chaffetz with Capitol Hill reporters.
Bannon said after getting the White House job Sunday: 'We had a very successful partnership on the campaign, one that led to victory. We will have that same partnership in working to help President-elect Trump achieve his agenda.'
Trump will take office with his staff in January.