A pop star, a rap star, just what category does we suppose to fit Drake in? Drake is king of Billboard’s 2018 year-end charts, as the superstar leads the year-end Top Artists ranking. The 32-year-old rapper-singer is the first rap act to be the overall top artist of the year since 2005 and just the third rap artist to lead the category. Billboard’s year-end music recaps are based on chart per…