Fox News founder Roger Ailes, who died Thursday at the age of 77, was one of the most (if not the most) controversial and influential news executives in American history. Ailes changed the way people watch news in this country, polarizing the market.

Before Ailes helped launch Fox News in October 1996, television news was not outwardly ideological. There were the network news channels (ABC, CBS and NBC) and one major cable news channel (CNN). None of those made explicit partisan appeal a priority. Sure, there were opinion programs (“Crossfire,” “The McLaughlin Group,” etc.). But they were usually small parts of a larger, non-ideological programming lineup, and even those shows tended to feature a mix of viewpoints.

The lack of a liberal or a conservative channel helps explain why Democratic and Republican voters really didn’t have a favorite network back in 1996. The Washington Post asked television news viewers what their main source for campaign news was in November 1996, just as President Bill Clinton was winning re-election by besting GOP candidate Bob Dole. And every network’s audience mirrored the nation fairly accurately: Each had a few more Clinton than Dole supporters just as the country had more Clinton than Dole voters.

Ailes saw an opening. Republicans had long believed that television news was biased against them. Fox News was billed as a corrective, launching with the slogan “fair and balanced” — a signal to conservative viewers that the network would be “fair” to Republicans, unlike other news outlets. He stocked Fox’s prime-time lineup with right-leaning commentators like Bill O’Reilly and Sean Hannity.

On election night in 2004, Fox News’s audience was bigger than any other cable network’s, and its 8 million viewers were more than triple its election night audience from 2000. It was clear that Ailes’s message was working. Republicans were tuning in to Fox News in massive numbers. According to post-election Pew Research Center surveys that asked voters what television network they got their campaign news from in 2004, 2008 and 2012, Fox News became the home for a plurality and eventually a majority of Republicans. After the 2016 campaign, a majority of Donald Trump voters told Suffolk University that the TV news network they trusted the most was Fox.

Ailes’s Fox News also caused a ripple effect in the news industry. As Fox News viewers supported Republican presidential candidates overwhelmingly, viewers of the other cable and network news channels were much more likely to vote Democratic in presidential elections. This has led to a polarization of the American TV news audience.

DEMOCRATIC EDGE AMONG THOSE WHO WATCH OR TRUST A CHANNEL MOST CHANNEL 1996 2004 2008 2012 2016 ABC +11 +7 +26 +5 +25 CBS +14 +8 +38 +31 +37 CNN +3 +32 +50 +44 +47 Fox News N/A -62 -49 -70 -66 MSNBC N/A +28 +56 +73 +70 NBC +9 -4 +28 +46 +30 News viewing has become more polarized since Fox News debuted Democratic edge is the percentage of viewers who voted for the Democratic presidential nominee minus the percentage who voted for the Republican nominee. In 1996, 2004, 2008 and 2012, voters were asked what their main television news source was. In 2016, voters were asked which news network they trusted most. There was no such poll in 2000. Sources: Fox News, Suffolk University, Washington Post

Fox News even gained an imitator: MSNBC. Seeing Fox News’s success on the right, MSNBC lurched leftward in the mid-2000s. It seems to have paid off. In the December 2016 Suffolk University poll, those who said MSNBC was their most trusted news source were almost exclusively Clinton voters in the same way that those who chose Fox News were almost exclusively Trump voters. With Trump in the White House, whether or not they admit it, MSNBC is riding the Ailes model of opinion programming to record ratings.

Ailes, though, wasn’t at the helm of Fox News to see MSNBC’s recent success. He was forced out of his job as chairman and CEO last year after being accused of sexual harassment by many women. Ailes was also accused of allowing a workplace culture in which racial discrimination and misogyny went largely unpunished. Shortly after Ailes’s ouster, O’Reilly — his most successful star — was also pushed out over allegations of sexual harassment.

The circumstances of Ailes’s exit from Fox will cast a shadow over his news career. His actions with employees and how he changed Americans’ news consumption are, at the end of the day, both part of the trail he left behind. He will, and probably should be, remembered for each.