AKG is an acronym for "Akustische u. Kino-Geräte", which (so I'm told) is German for "Acoustic and Cinematography Equipment" (we all remember the S-Gerät, the 00000, do we not, heh heh heh?). They are a Viennese company which makes microphones and headphones. Their web site (www.akg-acoustics.com) says that they dropped the film equipment business in 1965 because the audio gear was more profitable. Nowadays, they call themselves "AKG Acoustics".
They claim to have produced the first microphone with a cardioid pattern in 1953. "Cardioid" means that a two-dimensional graph of the mic's gain in various directions is vaguely heart-shaped: It is most sensitive to sounds in front of it, less sensitive to those behind. In other words, it's somewhat directional, and that's a darned good thing in a microphone. They seem to be proud of it; AKG's corporate logo is three cardioid pattern outlines superimposed in a radially symmetrical trefoil pattern. It's rather attractive.
They sell both cheap microphones and high-end ones listing in thousands of dollars. The price range of their headphones isn't quite so broad.