Who won wwii?

The best answer to the question "Who won WWII?" is probably "Hugh Dowding". He was the head of fighter command in the RAF before and during the Battle of Britain. He was a brilliant theorist who designed a very complex system of co-ordination and command that allowed the fighters under his command to out-fight the Luftwaffe even though they were significantly out-numbered. (This was easily as important as radar, but Dowding funded the development of radar too.)

If the Germans had been able to destroy fighter command, they would have been able to destroy the Royal Navy. If the Royal Navy had been destroyed, the British Army would never have been able to stop an invasion (they had no heavy weapons left after Dunkirk.) With Britain in German hands, there would have been no need to keep many troops in Western Europe and North Africa would have been a "walk over" for the Italians---so no Montgomery/Rommel sea-saw battles. Without the Royal Navy and merchant marine, there would have been no convoys to Russia with needed supplies. Without this support from Britain, Russia may very well have fallen to the Germans.

And even if the USA had entered the war against Germany and Russia had managed to survive until then, with no Britain to serve as a staging ground for invasion plus "unsinkable aircraft carrier", it might have been unable to beat the Germans too.

Finally, Dowding wasn't simply just one person who did a job that anyone could have. He was very unpopular with the "high brass" in the RAF, who thought that fighters would just be a "side show". In fact, he was forced into retirement shortly after the end of the Battle of Britain. So if there was any one man who's personal qualities had the most to do with winning that war, it may well have been Hugh Dowding!