Koichi Zenigata (usually called Inspector Zenigata) is an incredibly talented, yet often bumbling police officer who has made it his life's goal to capture Lupin III.
Inspector Zenigata was conceived as Lupin's arch rival to create a "human Tom and Jerry".
Monkey Punch has said that he believes the Lupin III story can never end but that if he had to, both Zenigata and Lupin would have to end as equals. They would either both fail, both win or both get very old.
Throughout the franchise, he has been portrayed as both a serious and competent police inspector and a bumbling, overzealous Lupin chaser. Although every incarnation of him has both of these qualities, the level of seriousness and incompetence varies. In the Green Jacket and Fujiko Mine Series, he is portrayed as more stern, whereas in the Red and Pink series as well as a majority of the TV specials and movies, he is much more goofy.
Zenigata is widely respected among his fellow officers at Interpol as an expert criminal catcher. He was able to discover security flaws and took down countless gangs and criminals long before he met Lupin.
Zenigata tends to be impulsive. This is probably due to his strong sense of justice and honor which others often consider old fashioned. Unlike most other officers in the police force and Interpol, he is resistant to bribery and is often offended when someone attempts to bribe him.