Melting Media is right on the money.
Although Little Walter was not the first harp player to use amplification, he was the first to make use of the sonic possibilities of a mic and amp to create a new voice for the instrument.
Many Chicago bluesmen who worked contemporaneously with Little Walter have claimed that Big Walter was actually a superior harp player, but that Little Walter had a better sound.
However, having heard hundreds of cuts by both, I'll still say Little Walter was, and is, the master.
His influence on later harp players is unsurpassed by anyone (although Sonny Boy #2 is a close second).
His accolytes such as George "Harmonica" Smith, Junior Wells, and Rod Piazza have, in turn, influenced another couple of generations of harp players.
Coincidentally, I just (finally) framed eight posters of harp players I got from Hohner about twenty years ago. The poster for Little Walter has the headline;
"He ran away from home before he was nine, played on city street corners until he was sixteen, and died from a fight when he was just thirty-eight. no wonder he played the blues so well."