Hall's voice was a blue-eyed soul instrument so pure it earned the respect of the Temptations -- he sang with them on Live at the Apollo. Oates' guitar and harmonies were the anchor. They were too rock for r&b, too r&b for rock, and too successful for either genre to argue.

Their 1973-1984 run is one of the most successful in pop history. The mustache became iconic. The songs became permanent. Hall still performs; Oates has moved on to other projects. But the records -- those impossibly catchy, immaculately produced records -- are the sound of two guys from Philly who figured out the formula and never stopped refining it.

Hall & Oates -- the most successful duo in pop history. Six number ones. Daryl's voice. John's mustache. The songs are permanent.