Blader DJ (Also known as DJ Jazzman) is the referee of the Beyblade manga, anime, and game series. Every Blader DJ is different in another country.
He is a cool announcer with a bandanna and appears throughout all the series of Beyblade. He calls the bladers to begin matches by saying the all important 3-second countdown phrase before saying "GO! Shoot!" in the Japanese version or "Let It Rip!" in the English version. He also comments on what's happening in the battle for the audience and viewers at home. At the end of Volume 14 of the manga, Daichi took over as the referee.
It seems he is still the referee in Metal Saga . Making him the only character to appear in both series. http://beyblade.wikia.com/wiki/Blader_DJ