Rupert Murdoch launched Fox News with the expressed idea of finding a niche in the US media market that would be competitive with the established media giants. His most immediate background was in the U.K. where he launched SKY News to compete against the British government's monopoly called the BBC. He was very successful there.
In the U.S. market the Democrats had controlled both Houses of Congress and the Presidency when Fox News was first being formed. That, along with the very Leftist tilt of the American media was tantamount to a government run monopoly on news reporting.
The 1994 midterm elections changed that and then just a bit later Fox News went live.
The primary faces on FNC are deliberately intended to "lean right." That's been Fox's strategy all along. Murdoch and Roger Ailes are going for the audience that is turned off by all of the liberal media's rants. The fact that this in turn appears to be the largest segment of the audience, well... that just shows where America is really at politically.
Even with the fact they are in fewer homes than CNN and MSNBC (see PO's post above, for example), Fox still overwhelmingly beats their competitors like a drum.
I say "kudos" to Murdoch and Ailes. They saw an opportunity to compete against what was essentially a fascist* monopoly and they have done so successfully.
*
Fascism: a political philosophy, movement, or regime (as that of the Fascisti) that exalts nation and often race above the individual and that stands for a centralized autocratic government headed by a dictatorial leader, severe economic and social regimentation, and forcible suppression of opposition.