The Voice began airing on April 26, 2011, as a spring TV season program. The show proved to be a hit for NBC and was subsequently expanded into the fall cycle when season three premiered on September 10, 2012. The series employs a panel of four coaches who critique the artists' performances. Each coach guides their teams of selected artists through the remainder of the season. They also compete to ensure that their act wins the competition, thus making them the winning coach. The original coaching panel consisted of Adam Levine, Blake Shelton, Christina Aguilera and CeeLo Green. Shakira and Usher took the places of Aguilera and Green in seasons four and six. Similarly, Pharrell Williams and Gwen Stefani replaced Shakira and Usher in season seven, with Williams permanently replacing Green in the eighth season