Any successful artistic collaboration is going to rely to some degree on serendipity, but Gnarls Barkley’s “Crazy” seems an especially uncanny intersection of timing and talent.

Though the partnership between producer Danger Mouse– fresh off the success of The Grey Album, his Jay-Z/Beatles mash-up– and Goodie Mob rapper/soulman Cee-Lo Green seemed like an intriguing match-up from the start, it hardly seemed like a recipe for an instantaneous worldwide smash hit.

Yet from the time it first appeared on the group’s website, “Crazy” became the virtual definition of a viral hit single, eventually becoming the first song to reach #1 on the UK charts solely through download sales. It went on to become the most played song 2006.

The song was originally a demo by Cee-Lo Green for girl group The Pussycat Dolls, as confirmed by lead singer Nicole Scherzinger but they instead chose the song “Don’t Cha” and released it as their lead single.