This name refers to multiple unrelated artists:
1. Alex Giannascoli--whose stage name was "Alex G" and is now "(Sandy) Alex G"--is a multi-instrumentalist from Philadelphia that has studied at Temple University, serving as a member of The Skin Cells. In general, he works as a guitarist and singer. You can check out his Facebook page at: https://www.facebook.com/sandyalexg and his bandcamp at https://sandy.bandcamp.com/
2. Alex G is a pop musician known for her work uploaded on YouTube and Facebook, most of it covers of modern pop rock. For more information, see: http://www.youtube.com/user/AlexGMusic7 .