For a great deal of the 1930s, Don Bradman was considered the most famous sportsman in the world. By any measure – stats, acclaim – it appeared to be a straightforward decision. The same could be argued for Mohammad Ali in the 1960s or Lionel Messi in the 2010s. But when, exactly, did they take their titles, from whom, and when did their reigns come to an end? For boxers it might be possible to narrow it down to the actual date, but for other sportsmen – and women – it is more difficult. Athletes have been feted for their sporting prowess since ancient times, and since the advent of professional sport in the early 18th Century there have been champions celebrated throughout the world. This book aims to give a clearer idea of who was – at any point in time – the greatest athlete in the world – even if the world was unaware of it at the time.