'Lightning' Bolt ready to blaze history-making trail again in South Korea

Usain Bolt, the world's fastest man, leads a powerful group of Jamaican sprinters into the World Athletics Championships but a repeat doping positive by Steve Mullings has cast a steroid shadow over the squad.

Bolt, the reigning world and Olympic double sprint champion, has lost only twice in his professional career and will be favorite to defend his 100m and 200m crowns in South Korea, and seal the same status for the 2012 London Olympics.