Donald Love of Grand Theft Auto fame certainly qualifies. While Grand Theft Auto III only vaguely alludes to his monstrous tendencies, Grand Theft Auto: Liberty City Stories sheds some light on his true personality. He will truly do anything to make money, including having Toni murder his mentor Avery Carrington just to steal his plans, as well as a news reporter that witnessed the murder. Did I mention what he does with the bodies? His most monstrous moment is when he orders Toni to sneak underneath the Fort Staunton section of Staunton Island and blow it to smithereens, likely causing the death of thousands of people. This action also explains the existence of the construction site in GTA3.
That reporter you mentioned weren't a saint either. Ned Burner, posing as a priest in a confession booth, got Toni (who was seeking redemption for his sins, ironically) to wreak havoc on the streets in a fire truck (killing countless civilians) so he could be the first on the scene to write a scoop about it, kill 3 celebrities who gave interviews to rival media institutions, kill a federal witness to a doping scandal and pull off a diamond heist. Damn, Toni Cipriani probably commits the greatest canonical atrocities of any GTA protagonist to date thanks to the orders of these two men.