Thank you for responding!  Glad to hear about MacArthur; my grandfather was a Marine who landed at Incheon.  I am interested to hear if Lewis Burwell ("Chesty") Puller is well known.  My grandfather personally met him :)

I think most famous American in Korea is Barack Obama

because  he is president of America korean can see him in news or internet and many things

other famous Amarican is general Douglas Macarthur he is hero in south korea because  

in korean war(1950~1953)

south korea was losing against north korea

but when 1950-9-15 general Macarthur attacked incheon 

From that time south korea was started winning

So, Macathur is hero in korea,korean can see his picture in hystory book and we study what he did in korean war

And korean know a lot of American movie star or politician or singer and band because development of internet So, I can't typing however korea know many many Americans