I’m reading, among other things, Bill Bryson’s Mother Tongue. He writes:
The new settlers in America obviously had to come up with new words to describe their New World, and this necessity naturally increased as they moved inland. Partly this was achieved by borrowing from others who inhabited or explored the untamed continent. From the Dutch we took landscape, cookie, and caboose. We may also have taken Yankee, as a corruption of the Dutch Jan Kees (“John Cheese”). The suggestion is that Jan Kees was a nonce name for a Dutchman in America, rather like John Bull for an Englishman, but the historical evidence is slight.
I find this interesting because, as it happens, John Cleese‘s father’s surname reportedly was “Cheese” before he joined the British Army in 1915, and his son could have easily been John Cheese.