For sure, Luffy from One Piece is strong, but it is also possible that there are people capable of defeating him. Inside the One Piece world, characters like the Yonko and Admirals would pose a serious threat by virtue of their devil fruit powers and Haki. Take, for example, Big Mom or Kaido with his incredible strength or the Admiral Akainu using Logia-type Magma Fruit it is a real menace in Groups From other anime, Naruto's Uchiha Madara and Dragon Ball's Goku each have the kind of brute force that may or may not beat Luffy.