Explanation: Admiral Yi Sun-sin of Korea was most famous for fighting off two Japanese invasions in the late 16th century AD. His sharp tactical acumen and ability to judge the capacity of his men, and his enemy, led his to numerous stunning victories at sea over the invading Japanese forces.

… but before he was an admiral, he was a landlubber! As military command was not always strictly divided between naval and land careers in many pre-modern polities, Korea included, Yi was initially a cavalry officer stationed on the northern border against the nomadic Jurchen tribes. He experienced stunning success there too, repeatedly repelling the Jurchen, and even totally destroying an invading Jurchen army and capturing their leader in combat.