Gillian B. Loeb was the corrupt Commissioner of the GCPD. He was killed on Christmas Eve by The Joker under the guise of Sionis.
Biography
Batman: Arkham Origins
Loeb had ties with crime lord Black Mask and ran operations with Sionis in consideration.He once tried to have the police make false accusations of then-Captain James Gordon, but these fell through, and once considered having Gordon murdered, although Black Mask had to talk him out of it. Eventually, he had Harvey Bullock try to dig any dirt on Gordon.
Loeb eventually made a speech conference on Christmas Eve regarding the impending execution of Julian Gregory Day after he was arrested. However, he dismissed any questions from the audience after one of them inquired the rumors that the GCPD wasn't actually responsible for Day's apprehension (the implication being that Batman was responsible).
That same night, Blackgate Prison was broken into by Black Mask's men, and Loeb was taken hostage. Loeb questioned whom he thought was Sionis about his actions. The latter replied that things had changed, and that he was starting with a new slate, one that Loeb wasn't on. A protesting Loeb was then thrown into the gas chamber, where he died from the poisonous fumes.