a critic or teacher of music characterized by timid and excessive reliance on rules; more broadly, a pedant
"That beckmesser can't hear the genius because he's too busy criticizing."
About the Word:
The operatic character Sixtus Beckmesser made his stage (and linguistic) debut in Richard Wagner's Die Meistersinger von Nürnberg. Wagner's Beckmesser was a nervous and narrow-minded clerk whose devotion to the rules made him both a pedant and a musical philistine.