#4 Rory Macdonald
Rory Macdonald was always regarded as the heir-apparent to Georges St-Pierre's UFC Welterweight throne. After all, the latter had taken Macdonald under his wing at the world-famous Tristar Gym, and 'Rory Mac' had a great ascent towards the upper-echelons of the UFC 170-pound division.
However, Macdonald suffered a couple of losses to Robbie Lawler, and although he did win a few fights in between, the Lawler fights were incredibly brutal and are said to have taken a huge toll on the bodies of both fighters. Nevertheless, following a decision loss to Stephen Thompson, Macdonald signed with Bellator MMA.
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Macdonald subsequently won the Bellator Welterweight Championship, and now holds wins over the likes of Paul Daley and Douglas Lima -- the latter of whom Macdonald beat to win the title. Although Macdonald's most recent venture of moving up to challenge Bellator Middleweight Champion Gegard Mousasi didn't work out well for him; the former is still considered to be one of the best MMA fighters today.