Chuck! Pretty sure it was the evolution of MMA, age, and a lack of desire (in that order) that broke him. This time however he may break Tito, which is fun and games for all the family.
And not exactly UFC related but I would have to say Andrei Arlovski. After getting "Fedor'd" it would seem hes not quite himself. He's only had one fight since (The KO loss to Rogers) so there is definitely still hope.
There are others that probably fit the bill much better for me but AA came to my mind first.