He was a key player in getting Donald Trump into the White House and now he'll have the president-elect's ear as he navigates one of the most controversial presidencies in modern history.
Bannon has been a shadowy figure on the campaign trail, but his new high-profile position in the Trump administration will change that. Democrats have been protesting his appointment with the Twitter hashtag #StopBannon, saying he's a racist, anti-Semitic abuser.
Here's what you need to know about Bannon.
In August, a 2007 court filing emerged showing that Bannon's ex-wife accused him of making several anti-Semitic remarks, according to NBC News.