Darkel was scheduled to be a main character in Grand Theft Auto III, but he was removed during the game development. He was intended to be voiced by the late Bill Fiore, of Tales from the Darkside fame.
Removal from GTA III
Rockstar did not reveal for several years why Darkel was removed from the game. It was speculated that he was removed due to the 9/11 attacks. Despite being taken out, Darkel remains listed in the GTA III manual credits and the character texture remains in the game's data files.
A group of tramps with molotovs can be found in the tunnel that connects 8-Ball's bomb shop in Harwood to the rear of the Supa Save! in Portland View, supposedly remnants of Darkel's "gang" - a Liberty Tree article also alludes to a rise in tramp-related assaults. Darkel was supposedly meant to live underneath the Callahan Bridge, where he would give the player missions.
In a Q&A, Rockstar claimed that Darkel was removed because he did not totally fit with the rest of the game. In this Q&A Rockstar denied that Darkel was removed due to 9/11, and denied the rumor that one of his missions was going to be blowing up a bus full of school children. 
Rockstar confirmed that Darkel would have appeared in five missions, but only the following can be confirmed:
- I Scream, You Scream (Boss; Replaced by El Burro in the final version of the game)
- Love Hurts (probably replaced by the mission Love's Disappearance)