He is perhaps one the most critical individuals who affected the human history so profoundly. Why?
Why Yi Sunshin is so important to the whole human history?
If Yi was not born or failed to defeat Japan in around 1600, the whole world would have changed fundamentally.
1. The human history as we know has been dominated by Europeans in the last several hundred years.
2. By 1600, the super powers of the world was not any European nation. It was China, Japan and Korea in terms of technology, population, and military.
Europe was catching up fast in size and technology in the previous hundreds of years.
3. Japan was ahead of China and Korea in military experience due to internal fights and trading with Western countries.
4. Japan could annex Korea in 1600 were it not for Yi sunsin.
5. If Japan managed to subdue Korea, they would have invaded China as they have planned, then or later.
6. If they succeeded, the world as we see would have been very different. Eastern Asian superpowers would have competed aginst the west and probably surpassed them in terms of military power. The whole history would have gone quite differently.
7. Even if they failed to invaded China successfully, they could have left their influence over Korea. In the subsequent decades, Japan would have stimulated China to be ready to cope with Western imperialists.
8. Admiral Yi, single handedly, turned the huge historical tide with an inexplicable ingenuity. The whole event was something that is almost bizzare.
9. If he was not present at that time at that place (as Yi in Korean standard was an oddity in many ways), the whole East Asian history would have changed. Subsequently, the very big forces of the human development would have gone in a very different way. China was defeated by UK and many other Asian countries were colonized by the West. There was a huge distortion of perspectives in the minds of billions of people on Earth due to the last hundred years' European dominance.
10. The world would have had a very different geopolitical and cultural map that is so profoundly affecting everyone on Earth. Perhaps we do not have McDonald or Starbucks at all, for ever. We would not use English as an international language. There would have not been be so much racism as we saw either as Eastern way of colonization is fundamentally different from Europeans who are based on absolute divinity religions such as Jewdaism and Christianity which produced fascistic, competitive, and uncooperative culture (as you see in the conflict between the single deity Christian west and muslims)
To exaggerate the situation and give you some visual impression:
Yi sunshin must have made all the Japanese generals, shoguns, and kings flabagasted. It was like present USA prepares a war with 5 aircraft carriers, 500 stealth bombers, military satellites and 100,000 ultra hightech special forces to strike Canada. They planned it for years with the best military minds. And they got defeated in every battle by a small fleet led by one individual who was not even supported well by his own country and nearly died of torture during the 7 years of war. And the USA retreats utterly defeated begging Canada to let them go back home alive. The historical happenning in 1590s was as bizarre as the above.
The most remarkable thing in the whole historical oddity is that it was mostly to one single person's integrity, courage, dedication, cultured mind, and sacrifice under the strong sense of justice, conviction, and belief of humanity and peace.
Many people get shocked by his continuous success in strategy and battles overcoming such difficult situations. However, it is not surprising at all once one understands the mental quality he had and exercised all his life. It is a story of an unusual level of civilized and rational judgement and way of life.