This question arises from arguments people have been having about Phelps not being as 'great' an olympian as Sir Steve Redgrave. In a sense I'm inclined to agree. There are a lot of swimming medals available and the practicalities of the sport mean that it's possible to get loads of them if you're good... see also gymnastics.
I suppose to sort out the greatest ever olympian we'd need to determine coefficients for each event and then get
olympic greatness = sum of(result x coeffiecient)