On April 6, 1973, Ron Blomberg of the New York Yankees became the first designated hitter in Major League Baseball history when he faced Luis Tiant of the Boston Red Sox. Blomberg walked. But history had been made.

It also spawned a debate that still rages this day in MLB: To DH or not to DH?

The designated hitter, a regular player that bats in the lineup instead of the pitcher, is a standard rule in the American League. The National League does not use the DH.

The rule has had advantages for players who weren't great fielders. It made all-stars out of players such as Seattle's Edgar Martinez and Boston's David Ortiz. It's also been used by AL teams to entice older free agents as a way to extend their careers.

The DH has also altered rules for the World Series. Games played in the American League parks will use the DH, it's not used in the NL parks. The same rules apply during the regular season when interleague play takes place.

There is debate within MLB to unify the rules of the two leagues, with either the American League returning to its pre-1973 rules and have the pitcher hit, like the National League or the National League adopting the DH.

MLB hands out an award for the most outstanding DH for the season. The award is named after Edgar Martinez.

More Info: en.wikipedia.org