Harmony Smurf (original French name Schtroumpf Musicien) is one of the main characters of the Smurfs comic books and the Smurfs cartoon show. He appeared on the show up until the Season 9 premiere episode, "The Smurfs That Time Forgot".
Harmony is the worst musician in the Smurf village. His main instrument is his trumpet, which is completely off key. In fact, he's something of a multi-instrumentalist; in "Smurphony In 'C'" he was given the opportunity to try other instruments when the other Smurfs were trying to figure out whether a different instrument would make any difference. They let him play the lute, the trombone, the harp and the harmonium, all of which ended up sounding really off key. It all culminated when Brainy Smurf handed Harmony a triangle, and after Harmony struck the instrument, the tone was so off key that it fractured the glass in Brainy's glasses. A final attempt had him conducting the orchestra, resulting in everybody playing off key.
Everytime Brainy or Papa Smurf is announcing something, Harmony plays his trumpet so that the others would know, so he's not entirely bad at this job. Also, it seems like Harmony is in charge of the wake-up calls for the other Smurfs.
While he may be the musician, there is a chance Harmony either is tone deaf or finds his own music to be masterpieces. In one episode, he wished for his trumpet to play better, but threw it away because it didn't make a "good sound", although it sounded very pleasant. Despite his awful skills when it comes to playing instruments, it seems that Harmony is actually a great singer as seen in "A Mere Truffle", where he sang a song about his love for truffles.