The duel between Miyomoto Musashi and Tsukahara Bokuden
Musashi was a dispossessed samurai who was credited with developing the two-sword method of fighting.
Lost in the mountains, Musashi encountered an old man who offered him shelter at his home. When Musashi boasted of his abilities, the old man laughed at him. Musashi became enraged and attacked the old man, who parried every stroke using nothing but a saucepan lid.
The old man was none other than Tsukahara Bokuden, a legendary swordsman, who eventually taught Musashi the finest points of the art.