The term Ultimate Fighting is a bit of a misnomer. The UFC, or Ultimate Fighting Championship, is a fight promotion that has Mixed Martial Arts fights. People regularly confuse this and refer to the entire sport as Ultimate Fighting.
Mixed Martial Arts is a professional fighting sport that combines the most effective techniques from a variety of fighting forms. Many traditional martial artists attempted to use their arts in the early UFC matches and were very dismayed to the lack of effectiveness of their arts.
Over the years ineffective, flowery, and convoluted techniques were burned away and what was left was a combination of Muay Thai, Boxing, Wrestling, Judo, and Brazilian Jiu-Jitsu. There are rare exceptions where techniques from other arts are used but for the most part only the aforementioned martial arts have proven themselves effective in real fighting.
Modern competitive athletes in the sport are very skilled in the disciplines necessary for MMA competition. The days of fighters that were only good in one skill set are over. In order to make a successful attempt at Mixed Martial Arts fighting an athlete must be excellent on the ground, in clinch, and on the ground.