Straight Outta Compton saw The D.O.C. (real name - Tracy Lynn Curry, born June 10, 1968, and a member of the hip hop group Fila Fresh Crew) while only working as a guest, rapped the opening verse, and wrote some lyrics for Dre's most likely.
The one guest is The D.O.C., who raps the opening verse of "Parental Discretion iz Advised." The D.O.C. (guest)  rapping (one song) Tracy Lynn Curry (born June 10, 1968), better known by his stage name the D.O.C., is an American rapper, songwriter, and record producer. In addition to a solo career, he was a member of the hip hop group Fila Fresh Crew and later collaborated with gangsta rap group N.W.Awhere he co-wrote many of their releasesas well as Eazy-E's solo debut album Eazy-Duz-It. wrote some lyrics, perhaps mainly Dre's lyrics, Cube wrote some of Dre's lyrics and nearly all of Eazy's lyrics. 
