From Rap Dictionary
The D.O.C., born Tracy Curry, was one of rap's most promising new voices because of his association with N.W.A. and was at the height of his career after penning lyrics and contributing vocals to the group's revoloutionary album, Straight Outta Compton. In 1989, The D.O.C. then released his Dr.Dre-produced debut album No One Can Do It Better. Fans loved his sharp delivery and deep deep charismatic voice. He was easily one of the fiercest lyricists that the West Coast had ever witnessed--a combination of Ice Cube's scowling aggressiveness but balanced with a sophistication that would have rivaled KRS-One at his best. With a ragga-tinged flow, he could drop lyrical bombs with fury on "It's Funky Enough" or sublimely style for "The Formula." Dre supported The D.O.C. with a bevy of funk-laden tracks that were pre-Chronic, meaning that the feel was rough and rugged vs. wet and sticky.
Not long after his debut album was released, he tragically lost his vocal chords in an auto accident, which resulted an end to his career. Had his voice survived, there's little doubt that The D.O.C. would have become one of Cali's greatest MC's ever. All the supporting evidence is on his debut album.
After a split with Dr Dre and Death Row in 1996, over a lack of payment, the DOC took all the raps and ideas that he had written for Dr Dre's forthcoming solo album Helter Skelter (which was supposed to be with Ice Cube) and released the album on his own. The album is patchy at best and centers around a new world order. A single by Dre and Ice cube was released from this album - Natural Born Killaz, and the beats and raps are similar to that. After the doc left Death row Dr dre had no one to write his raps for him and so enlisted Sam Sneed and NAS to write them, a real change in dr dre's rapping style can be seen between 1997 - 1999 (when eminem becomes his main writer).
The D.O.C. contributed as a ghost writer for most of Dr Dre's raps, and for others on to NWA's Efil4zaggin Dr Dre's the Chronic and Snoop Dogg's doggy style. His complex lyrical style is one of the best in rap.