Doctor Sparrow first appears in "Conviction", where, as per the orders of the Senior Partners, he implants Gunn with absolute knowledge of all human and demon laws, demonic languages, golf techniques, and Gilbert & Sullivan compositions, thus making him the head of Wolfram & Hart's Legal Department.
Proceeding this, he does not reappear until "Smile Time", when Gunn discovers that he is losing his mental upgrades; not wanting to go back to simply being "the muscle" of Angel's crew, Gunn makes a deal with Sparrow and gets a sarcophagus out of Customs, and thus the upgrade is improved and made permanent.
In "Shells", he is revealed to be a worshiper of Illyria, and was conspiring with Knox to resurrect it using Fred's body. Upon discovering this, Gunn assaults Sparrow, demanding knowledge of how to bring Fred back and eject Illyria from her body, but Sparrow calmly informs him that Fred's soul was completely destroyed when Illyria was resurrected; thus, Fred is indeed gone forever. After telling Gunn that he now has to live with the consequences of their deal, he is pistol-whipped by Wesley and subsequently tortured by Spike, ultimately revealing Illyria's plans.
He returns in the comic, Angel: Old Friends, in which he creates evil clones of the Angel Investigations team as he last saw them and sends them out to destroy the originals. Angel, Spike, Gunn, and Illyria effortlessly defeat the clones and track Sparrow down and ultimately, Angel's clone (the last one left alive), betrays Sparrow and destroys his work before dying himself.