No singer of the 2010s could compare to Adele in terms of sheer sales or stardom. Beginning with 21, her sophomore set from 2011, Adele existed in a different stratosphere than her British or American peers, selling tens of millions of her albums at a time when many musicians scrambled to get to a million. The key to Adele’s appeal lay in her sly, subtle interweaving of old-fashioned soul, confessional songwriting, and pop polish — diverse sounds tied together by her powerhouse vocals.