The title of "best runner" is subjective and depends on the criteria used for evaluation. Here are a few candidates often mentioned, each with their strengths:

• Usain Bolt:

  Considered by many to be the greatest sprinter of all time. He holds the world records in the 100 meters (9.58 seconds) and 200 meters (19.19 seconds). World Athletics profile of Usain Bolt

• Eliud Kipchoge:

  Widely regarded as the greatest marathon runner. He holds the official world record for the marathon (2:01:09) and ran a marathon in under two hours in an unoffical race. Eliud Kipchoge's website

• Hicham El Guerrouj:

  A dominant middle-distance runner. He holds the world records in the 1500 meters (3:26.00) and the mile (3:43.13). World Athletics profile of Hicham El Guerrouj

The "best" depends on whether you value speed, endurance, or middle-distance prowess.