UFC Middleweight Championship

Ultimate Fighting Championship (UFC) champions are fighters who have won UFC championships. At the time of the UFC's inception in 1993, mixed martial arts was unsanctioned in the United States, and did not include weight classes. Instead of the traditional championship model, the UFC held tournaments with the winner receiving a permanent appellation. In response to criticism from Senator John McCain that saw the loss of its television deal and the banning of the sport in thirty-six states, the UFC increased its cooperation with state athletic commissions and introduced weight classes in 1997, starting with UFC 12, and began introducing weight-specific titles.

The original codification for weight classes introduced only two divisions: heavyweight, which grouped together all competitors above 200 pounds (91 kg), and lightweight, which encompassed all competitors 199 pounds (90 kg) and under. At UFC 14 the lightweight division would be renamed to middleweight, though it would still encompass all fighters 199 pounds (90 kg) and under. The lightweight moniker would later return at UFC 16 with a new division consisting of those competitors 170 pounds (77 kg) and under. Two years later a fourth weight class, the bantamweight division, arrived at UFC 26 and included all fighters 155 pounds (70 kg) and under.

In 2000, the New Jersey State Athletic Control Board completely took over MMA regulation in its home state and developed new rules and weight classes that eventually became the de facto rule set for all mixed martial arts. The UFC realigned their weight classes to comply with these new regulations in 2001, beginning with UFC 31. At the time, this brought the total number of active divisions in the UFC to five: lightweight, welterweight, middleweight, light heavyweight and heavyweight.

...
Wikipedia