The international one-day game is a late twentieth-century development. The first ODI was played on 5 January 1971 between Australia and England at the Melbourne Cricket Ground. When the first three days of the third Test were washed out officials decided to abandon the match and, instead, play a one-off one day game consisting of 40 eight-ball overs per side. Australia won the game by 5 wickets.
That's the small history of how the one day international game evolved. From then, the game has improved vastly along with the aggression of the batsman to score run against the bowler.
Here are listed the five fastest half centurions(50 runs) in one day internationals