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Brock Lesnar vs. Frank Mir
When Brock Lesnar left professional wrestling to compete in MMA, drama was bound to develop.
After making quick work of Min-Soo Kim in Japan, Lesnar made his UFC debut against Frank Mir.
A confident heavyweight with championship experience, Mir was a good antagonist in the Lesnar story. Mir caught Lesnar with a kneebar at UFC 81. That helped create a feud that led to Lesnar and Mir headlining the historic UFC 100 fight card.
In their second meeting, Lesnar stopped Mir with ground-and-pound to become the undisputed heavyweight champion. A rubber match was proposed as recently as January, when Mir spoke with FoxSports.com, but a Lesnar return to the Octagon doesn't look like a reality right now.
Chuck Liddell vs. Tito Ortiz
It was a matchup that took a long time to put together, but Chuck Liddell and Tito Ortiz turned out to be great rivals once their fights were finally booked.
Ortiz initially backpedaled from fighting Liddell due to the fact that they were former teammates. However, Liddell insisted that he had no issues with fighting "The Huntington Beach Bad Boy" and accused Ortiz of ducking him.
The disagreement eventually developed some animosity between the two. When they finally met inside the Octagon, Liddell picked up two knockout wins over Ortiz.
Dominick Cruz vs. Urijah Faber
Rarely does the bantamweight division have a chance to stand out, but it did when Dominick Cruz and Urijah Faber met in a rematch during July 2011.
Faber and Cruz originally met under the WEC banner, where "The California Kid" submitted a young Cruz to defend his featherweight championship. When the tables were turned at UFC 132, Cruz's outstanding footwork helped him even the score in a decision.
Not long after, Cruz and Faber were chosen to coach The Ultimate Fighter (TUF) prior to what would have been a rubber match at UFC 148. It was a huge opportunity for the 135-pound class to gain popularity, but Cruz tore his ACL before the bout happened and still hasn't stepped into the Octagon.
Ronda Rousey vs. Miesha Tate
The rivalry between Ronda Rousey and Miesha Tate began under the Strikeforce banner.
With only four fights under her belt heading into their first meeting, Rousey was not viewed by Tate as a deserving challenger. However, before the first round came to an end, Rousey had Tate's arm twisted badly and came away with a submission win.
When Tate lost to Cat Zingano in her UFC debut, it looked as though a rematch would have to wait. However, a Zingano injury opened the door for Tate to coach opposite Rousey on The Ultimate Fighter, which only increased the dislike the female bantamweights had for one another.
At UFC 168, Rousey locked up another armbar against Tate, which might rid her of "Cupcake" for good.
Tito Ortiz vs. Ken Shamrock
When talking heated rivalries, Tito Ortiz and Ken Shamrock would be right up near the top.
However, against Ortiz, Shamrock was never able to back up his talk inside the Octagon. The MMA pioneer was stopped in all three of his bouts with Ortiz and only made it out of the first round on one occasion.
Ortiz and Shamrock helped produce one of the more entertaining TUF seasons, but the lack of competitiveness in their bouts keeps them out of the top 10.