The idea of Bradshaw going on to become a top heel in WWE would have been unfathomable to anyone who watched him and Farooq during the APA days of the Attitude Era, but somehow, someway, he pulled it off. Dropping the tag team gimmick (and his tag team partner), Bradshaw became John Bradshaw Layfield. And somehow, someway, JBL became WWE Champion.
SmackDown was trying to figure itself out in 2004. Brock Lesnar had left the company, Kurt Angle was relegated to general manager, and The Undertaker had just recently returned to his original Deadman gimmick. There was a lot of change, but one unexpected constant was JBL's title reign, which lasted for the majority of the year (and into the beginning of 2005).
JBL lied, cheated, retreated, and complained his way through that title reign, unwittingly finding himself surviving bouts against The Undertaker, Booker T, and Eddie Guerrero. Sure, it got stale and annoying the longer it went on, but it was designed to so that someone (John Cena) could finally put a stop to it.
We don't talk about JBL enough when it comes to solid bad guys, but the truth is that SmackDown fans in 2004 hated him - and they loved doing it.