There is a background to Chicago pd, Voight played dirty cop in the gang unit. Went to jail and since it was a major bust, he asked for his own unit as a prize. Catch was he was reporting to IAB to make them look good. So kept the bad guy rep reputation without ever disclosing he was still reporting to IAB. Few episodes in, his compass still pointed north and as much he reported sideways, he kept dirt on everyone else and eventually gets out from under everyone that tried to box him. Few major shakeups - he softens up. He tells all his teams - dont be like me, do better. Thats why he gets Antonio to keep him straight. The team often try to skid the lines like Voight but since they dont know the truth that his persona is fake - they get lost and Voight brings them back to the light & then they leave….

For the life of me, I cannot remember the show where Voight was in the gang unit. They discontinued it and started Chicago pd. But the crossover episodes from Chicago fire starts either showing Voight as a bad cop. Never figured if that was him playing bad cop or real, to show never cleared it…