Who was the first rapper to sell 1 million records?

Depending on whose figures you believe, the individual/group who has sold the most albums overall is either Elvis Presley or The Beatles. In terms of known, verified sales, the Beatles lead by about 5 to 4.

The highest-selling SINGLE album is Michael Jackson's Thriller. In terms of overall verified sales, he's at about 3 compared to that 5:4 ratio mentioned above, slightly behind Madonna (also about 3).