In October 1985, 20th Century Fox announced its intentions to form a fourth television network that would compete with ABC, CBS and NBC. The plans were to use the combination of the Fox studios and the former Metromedia stations to both produce and distribute programming. Organizational plans for the network were held off until the Metromedia acquisitions cleared regulatory hurdles. Then, in December 1985, Rupert Murdoch agreed to pay $325 million to acquire the remaining equity in TCF Holdings from his original partner, Marvin Davis. The purchase of the Metromedia stations was approved by the Federal Communications Commission (FCC) in March 1986; the call letters of the New York City and Dallas outlets were subsequently changed respectively to WNYW and KDAF. These first six stations, then broadcasting to a combined reach of 22% of the nation's households, became known as the Fox Television Stations group. Except for KDAF (which was sold to Renaissance Broadcasting in 1995 and became a WB affiliate at the same time), all of the original owned-and-operated stations ("O&Os") are still part of the Fox network today. Like the core O&O group, Fox's affiliate body initially consisted of independent stations (a few of which had maintained affiliations with ABC, NBC, CBS or DuMont earlier in their existences). The local charter affiliate was, in most cases, that market's top-rated independent; however, Fox opted to affiliate with a second-tier independent station in markets where a more established independent declined the affiliation (such as Denver, Phoenix and St. Louis). Largely because of both these factors, Fox in a situation very similar to what DuMont had experienced four decades before had little choice but to affiliate with UHF stations in all except a few (mainly larger) markets where the network gained clearance.
The Fox Broadcasting Company launched at 11:00 p.m. Eastern and Pacific Time on October 9, 1986. Its inaugural program was a late-night talk show, The Late Show, which was hosted by comedian Joan Rivers. After a strong start, The Late Show quickly eroded in the ratings; it was never able to overtake NBC stalwart The Tonight Show whose then-host Johnny Carson, upset over her becoming his late-night competitor, banned Rivers (a frequent Tonight guest and substitute host) from appearing on his show (Rivers would not appear on Tonight again until February 2014, seven months before her death, when Jimmy Fallon took over as its host). By early 1987, Rivers (and her then-husband Edgar Rosenberg, the show's original executive producer) quit The Late Show after disagreements with the network over the show's creative direction; the program then began to be hosted by a succession of guest hosts. After that point, some stations that affiliated with Fox in the weeks before the April 1987 launch of its prime time lineup (such as WCGV-TV (channel 24) in Milwaukee and WDRB-TV (channel 41) in Louisville) signed affiliation agreements with the network on the condition that they would not have to carry The Late Show due to the program's weak ratings.
The network expanded its programming into prime time on April 5, 1987, inaugurating its Sunday night lineup with the premieres of the sitcom Married... with Children and the sketch comedy series The Tracey Ullman Show. Fox added one new show per week over the next several weeks, with the drama 21 Jump Street, and comedies Mr. President and Duet completing its Sunday schedule. On July 11, the network rolled out its Saturday night schedule with the premiere of the supernatural drama series Werewolf, which began with a two-hour pilot movie event. Three other series were added to the Saturday lineup over the next three weeks: comedies The New Adventures of Beans Baxter, Karen's Song and Down and Out in Beverly Hills (the latter being an adaptation of the film of the same name). Both Karen's Song and Down and Out in Beverly Hills were canceled by the start of the 198788 television season, the network's first fall launch, and were replaced by the sitcoms Second Chance and Women in Prison.
In regards to its late night lineup, Fox had already decided to cancel The Late Show, and had a replacement series in development, The Wilton North Report, when the former series began a ratings resurgence under its final guest host, comedian Arsenio Hall. Wilton North lasted just a few weeks, however, and the network was unable to reach a deal with Hall to return as host when it hurriedly revived The Late Show in early 1988. The Late Show went back to featuring guest hosts, eventually selecting Ross Shafer as its permanent host, only for it to be canceled for good by October 1988, while Hall signed a deal with Paramount Television to develop his own syndicated late night talk show, The Arsenio Hall Show. Although it had modest successes in Married... with Children and The Tracy Ullman Show, several affiliates were disappointed with Fox's largely underperforming programming lineup during the network's first three years; KMSP-TV (channel 9) in Minneapolis-St. Paul and KPTV (channel 12) in Portland, Oregon, both owned at the time by Chris-Craft Television, disaffiliated from Fox in 1988 (with KITN (channel 29, now WFTC) and KPDX (channel 49) respectively replacing those stations as Fox affiliates), citing that the network's weaker program offerings were hampering viewership of their stronger syndicated slate.
The network added a third night of programming, on Mondays, at the start of the 198990 television season, a season that heralded the start of a turnaround for Fox. That season saw the debut of a midseason replacement series, The Simpsons, an animated series that originated as a series of shorts on The Tracey Ullman Show; ranked at a three-way tie for 29th place in the Nielsen ratings, it became a breakout hit and was the first Fox series to break the Top 30. The Simpsons, at 27 years as of 2016, is the longest-running American sitcom, the longest-running American animated program, and in 2009, it surpassed Gunsmoke as the longest-running American scripted primetime television series. That year, Fox also first introduced the documentary series Cops and crime-focused magazine program America's Most Wanted (the latter of which debuted as a half-hour series as part of the network's mainly comedy-based Sunday lineup for its first season, before expanding to an hour and moving to Fridays for the 199091 season). These two series, which would become staples on the network for just over two decades, would eventually be paired to form the nucleus of Fox's Saturday night schedule beginning in the 199495 season. Meanwhile, Married... with Children which broke ground from other family sitcoms of the period as it centered on a dysfunctional lower-middle-class family, whose patriarch often openly loathed his failures and being saddled with a wife and two children saw viewer interest substantially increase beginning in its third season after, in an ironic twist, Michigan homemaker Terry Rakolta lodged a boycott to force Fox to cancel the series after objecting to risque humor and sexual content featured in a 1989 episode. Married...'s newfound success led it to become the network's longest-running live-action sitcom, airing for 11 seasons.