For me its probably Tsukahara Bokuden (1490-1571), who popularised the idea of going on a ‘pilgrimage’ around Japan and challenging the best swordsmen to a duel. In his later life, he was probably the first renowned fighter to come up with the philosophy that not fighting shows more strength than fighting; Bruce Lee’s ‘art of fighting without fighting’ from Enter the Dragon was lifted from a story about Bokuden.

Tsukahara Bokuden: A Samurai Warrior Ahead of His Time