From Wikipedia:
Character History
Pre-Crisis on Infinite Earths, Bullock was a crooked police detective under instructions from Gotham City's Mayor Hamilton Hill to sabotage Commissioner Gordon's career. His method of doing so was to pretend to be exceedingly clumsy, thereby spoiling whatever Gordon was trying to do, seemingly accidentally. After inadvertently giving Gordon a heart attack, however, Bullock turned over a new leaf. His character later developed into a well-meaning cop who (probably) was exceedingly clumsy, similar to the later animated version. He also formed a close bond with Robin, based initially on their mutual love of old movies. Subsequent to this, he was a Bishop in the spy organization Checkmate.
Post Crisis
Post-Crisis, Bullock was perhaps the most controversial police officer in the Gotham City Police Department. His colleagues in the Major Crimes Unit will swear up and down that he is a good cop, despite his reputation for taking bribes, police brutality, and ties to organized crime being on the top. However, he also has elements of the earlier character including a fondness for doughnuts and a hidden sentimental streak. Bullock was loyal to Gordon from the start. Even before he made detective, he stayed by Gordon and helped him foil the Joker's plot to flatten Gotham City, without Batman's help. Bullock played (or was) the part of the 'bad cop', intimidating and threatening whoever needed it.