Vampires such as Angel (Buffy the Vampire Slayer) are naturally skilled at combat even upon being sired, able to fight with great skill and shoot with great accuracy even if they didn't have such skills as a human.
While she had poor fighting skills during her first year as a vampire, Harmony Kendall (Buffy the Vampire Slayer) began honing her instincts, allowing her to hold her own in combat.
The Fight (Cardcaptor Sakura) is a master of martial arts.
Batman (DC Comics) is a tremendously skilled master in mixed martial arts.
The Third Doctor (Doctor Who) was skilled at martial arts, particularly Venusian aikido as demonstrated here.
Hayato Furinji (History's Strongest Disciple Kenichi) a well known user of this ability.
Shang Tsung (Mortal Kombat) can mimic all fighting styles of the other fighters.
Like all Fighting Pokémon, Machamp (Pokémon) is a natural fighter.
Super Commando Dhruva (Raj Comics)
Colleen (Road Rovers) is a master martial artist
Martial Artist (Valkyrie Crusade) is master of all forms of martial arts.
Wuxia (Valkyrie Crusade)
Oogway (Kung Fu Panda) is the founder of Kung Fu, and considered to be its greatest master of all time.
Ryu Hayabusa (Ninja Gaiden) is the most powerful Ninjutsu master the Hayabusa Clan has ever produced with deep knowledge of other forms of martial arts.
Raidou (Dead or Alive) is one of the most powerful Tenjinmon Ninjas known.
Nomura Fudo (Busou Shoujo Machiavellianism) is an extraordinary martial art genius.
Stick (Marvel Cinematic Universe) is immensely skilled martial artist even at the age of 90.
Black Panther (Marvel Comics)
Deadpool (Marvel Comics)
Gamora (Guardians of The Galaxy/Marvel Comics)
Taskmaster (Marvel Comics)
Vision (Marvel Comics) has turned himself into a master martial artist.
Tryco Slatterus/Champion of the Universe (Marvel Comics)
Yoruichi Shihoin (Bleach) is one of the greatest Hakuda masters ever known in Soul Society.
Sosuke Aizen (Bleach) is a master warrior with tremendous skill in both Hakuda martial arts and Zanjutsu swordmanship.
Heihachi Mishima (Tekken) has tremendous skills in Mishima style Karate.
Ichijou Aoi (Choujin Koukousei-tachi wa Isekai demo Yoyuu de Ikinuku you desu!) has tremendous skills in martial arts particularly her mastery of swordsmanship.
Ikki Kurogane (Rakudai Kishi no Cavalry) is a martial art master who invented Blade Steal, a skill that copies his opponents martial arts techniques and adapt it into his swordsmanship...
...derived from his Perfect Vision that allows him to grasp his opponents' movements and predict their movements, personality, and thoughts.
Might Guy (Naruto) is the most powerful Taijutsu master in Shinobi history.
Originally watching his brother trained, Toki (Fist of the North Star) demonstrate his fighting ability by brutally beating a hunter who had killed his pet dog.
Each member of The Hateocracy (Boondocks) is a master martial artist despite never training a day in their in hate filled lives.
Despite being almost completely self-trained, Kyle Katarn (Star Wars) become one of the New Jedi Order's greatest lightsaber duelists.
Rock Lee (Naruto) has trained relentlessly to be a great Taijutsu master, capable of fighting the most skilled opponents using pure Raw Power and skill.