Michael Phelps (YouTube)
Cape Town - South African Chad le Clos' butterfly battle in the pool with American legend Michael Phelps shapes up as one of the most anticipated of the 2016 Rio Olympics.
Le Clos will attempt to go one better than his silver medal from London in the 100m butterfly - and defend his 200m title.
Standing in his way will be 18-time gold medal winner Phelps, appearing in his final Olympics.
So what does it take to become the all-time leading Olympic medal winner (with 22)?
Take a look...