Simplify the following text for a Grade 5 native English-speaking person.
Original: On October 7 , 2008 , his album Kind of Blue , released in 1959 , received its fourth platinum certification from the RIAA , signifying sales of 4 million copies .
Simplified: In 1959 he released an album called Kind of Blue which became very famous and popular . In 2008 it had sold 4 million copies .