Nivens was Harvey Bullock's landlord.
Nivens' worst tenant was by far Bullock. His lack of manners, intimidating behavior, slovenly habits, and the fact that he was the last in the building still on rent control made Nivens want to get rid of him.
He sent Bullock various anonymous threats, by mail and by phone, but he wouldn't budge. So Nivens took it upon himself to scare him, or kill him if need be. On his way from work, he surprised Bullock with a drive-by, but he missed.
Later, Nivens tried pushing him in front of the subway, but Bullock managed to roll to safety.
In the end, up to his breaking point, Nivens walked straight up to him, gun in hand and a mask on his face, but was too scared to take the shot. Batman stopped him, and Nivens confessed upon his unmasking. His mind finally snapped, he fell to the ground laughing hysterically and was taken away by Bullock, who then stated how ironic it was that he was actually thinking of moving anyway because of the bad neighborhood.