Georges St-Pierre and Lyoto Machida, both who have won belts in the UFC, were originally from a Karate background. For GSP it was Kyokushin, and Machida a Shotokan style. For Pierre he actually credits a lot of his takedown skills in the Octagon to Karate. He says his ability to leap in and out swiftly was developed through Karate. For Machida, he still practices his father's style of Karate: Machida Martial Arts Karate. This style was geared towards his father, Yoshizo Machida, dealing with larger opponents.
Aside from the physical tools, the mindset from Karate is something that has helped both Georges St-Pierre and Lyoto Machida.