A few famous WWE wrestlers started doing MMA, over the years. Only a few of them won important fights and win titles. MMA is very different from professional wrestling, although some professional wrestling techniques can be used in MMA.
Do not forget that professional wrestling has its root in catch wrestling which is a proper combat sports. Many famous WWE wrestlers have amateur wrestling backgrounds. These wrestlers often do well when they start doing MMA.
That is because they know how to fight for real. Most professional wrestling matches are scripted! Brock Lesnar is one of the most successful professional wrestlers of the world. He is also an MMA fighter. In fact, he is the most successful MMA fighter who is also a professional wrestler.
He is a former UFC Heavyweight Champion. Lesnar was at the Assiniboia Sports Celebrity Dinner & Auction in April. During the event he talked about why he keeps his contracts with the UFC and the WWE short. He said that he wants to jump between the two promotions. He can only do that if his contracts are short!