Darko Brevic was Niko Bellic's long-time antagonist, and the tertiary antagonist of Grand Theft Auto IV. Darko and Niko grew up together, and fought in the war (Niko's old friend Bernie Crane also joined). However, Darko betrayed Niko and Bernie for some reason, and killed all Niko's war friends! Fortunatley, Niko and Bernie survived. This was one of the reasons Niko moved to Liberty City, to find and kill Darko. Near the story's ending, Darko is found by a government agent under the name of United Liberty Paper Contact. Niko and Roman Bellic go to the airport and meet Darko. They have a long conversation, and Darko reveals he killed Niko's friends for $1,000! Niko, fighting back his tears, is very upset about this, and Darko's fate is left to the player. Kill Darko or let him live. If you spare him, Niko will feel a little better, but if you kill him Niko will tell Roman he feels "empty".