Fanatical red-earmuff-wearing anti-noise campaigner who determines that the only way to eliminate the noise of the world is to eliminate the world itself.
To this end, Pfister (the 'P' is silent) develops the silent explosive Nitrowhisperin. His other inventions include a presumably silent (or at least very quiet) shotgun, a silent phonograph record, sound-absorbing wood and a cuckoo clock with (as Maxwell Smart describes it) "laryngitis".
Pfister also operates Ye Oulde Pfix-It Shoppe where he maintains what he calls his "private air force" of homing pigeons to carry the explosive to important cities in the free and not-so-free worlds.
Note that he is called Albert Pfister in the episode but A. J. Pfister in the credits. The name of this article is an amalgam of the two.