A Western District uniformed officer.
- Alliterative Name: Bobby Brown.
- Characterization Marches On: A minor example, he has a shaved head in the pilot, barely noticeable under his cap. He sports a head full of hair in the rest of his appearances.
- Deadpan Snarker: Loves to joke about the job. After the tortured body of Brandon is discovered, he remarks it's the worst case of suicide he's ever seen.
- Functional Addict: Implied, he's very grateful of Jimmy for providing a box of beers before a stakeout and later they discuss how to deal with hangovers. Bobby says he can just throw up once or twice and goes to work without it having any negative effects.
- Headbutting Heroes: During the cutbacks, he starts a brawl with another police officer in the parking lot over the poor state of a vehicle he hands over.
- Seen It All: His dismay is complete when he sees McNulty arriving at a (potential) crime scene on a bus.
He first shows up as a narcotics officer working in the Western District, and is shot during a routine and small time narcotics bust. His gun is also stolen, which is a very big deal for police departments, leading Bunk on a wild goose chase to try to recover it. After recovering from his wounds Dozerman joins the Major Crimes Unit at the same time that Herc rejoins it.
A narcotics officer who serves in Carver's squad in the Western District. At the start he is often partnered with Herc, and the two share many qualities, including a brute force approach to the drug war. He's the one who inspires the nickname Hamsterdam when he compares the Free Zones to Amsterdam in front of the street dealers. He despises the Free Zones, however, calling it "moral midgetry" and is delighted whenever he has the chance to bust heads. He increasingly goes off the rails in seasons 4 and 5, becoming more brutal and aggressive, until he actually attacks a school teacher who asks Colicchio to just move his police car out of the way so the teacher can make it to his job. Carver is disturbed by Colicchio's complete lack of remorse and refuses to cover for him, getting Colicchio charged with both excessive force and conduct unbecoming a police officer.
- Dumb Muscle: Enforces drug rules by brute force, eschewing any subtlety or understanding of the streets, often to his detriment, including when he falls for a simplistic prank that winds up being the cause of his undoing.
- Jerkass: Look no farther than when Carver tries to do a faux pleasant exchange with Bodie.Bodie: And a very good evening to you, Officer Colicchio.
Colicchio: Go fuck yourself with a 40, shit breath.
- Kick the Dog: Assaulting a citizen during the course of a bad day is already pretty bad, but showing a complete lack of remorse long after he should have calmed down is when Carver decides In-Universe that Colicchio has passed the Moral Event Horizon.
- Police Brutality
- Rabid Cop
- Shell-Shocked Veteran: Busch was a marine who served 2 tours in Iraq, there are hints that Colicchio was also in the Armed Forces and he is certainly one of those who adopts what Colvin describes as a "soldier's mentality" to his approach as a cop.
- Took a Level in Jerkass: He starts out as a background character without much flavor, but he becomes more of an aggressive jerkass throughout the series until he outright qualifies for the Rabid Cop designation.
Walker: You think that hurts? [breaks one of Donut's fingers] You're so smart, lets see how easy you can boost a car now. [Breaks another finger]
A corrupt patrol officer in the Western District, he is feared on the streets because of his willingness to inflict Police Brutality on anyone from Omar to little kids, and to engage in acts such as robbing suspects before they are arrested. He clashes several times with the middle school friends focused on in season 4.
- Bad Liar: When several of the middle schoolers pay him back by covering him in yellow paint, (and Michael steals the ring he stole from Omar, who stole it from Marlo) Walker claims that he was jumped by an entire gang of Bloods who were delivering a declaration of war against the police. McNulty calls bullshit on the story and no one else seems like they buy it either.
- Base-Breaking Character: An In-Universe case for his fellow cops, some think his brutal, no holds barred methods of policing are the only way to keep street kids in line, while others (most prominently McNulty) think he's a piece of shit who shouldn't be on the force.
- Boomerang Bigot: Walker is black, but is perfectly willing to use racist terms and metaphors against the street youth, including one occasion where he tells the boys from season 4, who're in a nicer section of town eating some Chinese food "You're off the reservation".
- The Bully: An aggressive asshole who uses his position of authority to push people around.
- Chekhov's Gunman: He (or at least the actor playing him) has a short scene is season 2 when Bunk and the MCU go to bust The Greek's brothel. A couple of years later, and he suddenly reappears and becomes a recurring character for season 4.
- Corrupt Cop: Frequently steals from or brutalizes anyone from the streets, including taking money from Randy, stealing bootleg DVDs from Bubbles when Bubs tries to report being robbed, and taking the ring that Omar stole from Marlo before Omar is arrested.
- Dirty Coward: He relies on his status as a police officer to protect him from any potential payback for his actions, as most gangsters are reluctant to mess with cops due to the massive consequences. When faced with someone willing to stand up to him despite him being a cop, his tough guy bravado disappears.
- Disproportionate Retribution: Snaps several of Donut's fingers because of the paperwork that Walker would have to fill out thanks to Donut driving into other vehicles while on a joyride.
- The Dreaded: Anyone from the streets knows who Officer Walker is, and they're in no hurry to meet him.
- Hate Sink: Walker represents the type of cop that no one wants to meet: a corrupt and brutal scumbag who's only in it for himself.
- Jerkass: Eddie Walker is not a nice man. For further information, look at the rest of his character tropes.
- Karma Houdini: His worst comeuppance is having an outfit ruined when paint is tossed onto him, and losing a ring he stole from someone else days earlier. Maybe he also loses some of the tough guy swagger and respect he enjoyed among fellow hardliner cops, but that is implied at most, not directly said.
- Police Brutality: Breaks the fingers of a 6th grader who stole a car and went on a joyride simply because it meant that Walker would have to fill out extra paperwork.
- Would Hurt a Child: See Police Brutality.
A rookie patrol officer introduced in Season 3. Colvin gives him and another newcomer a much repeated speech about knowing the street and their sense of direction, instructing the two to carry compasses until they can always accurately tell which direction they're facing. During season 4 he's briefly paired up with McNulty when Jimmy reassigned himself to patrol, and the two catch a pair of thieves that have been robbing many churches in the district together. Afterward McNulty tells Bunk that he thinks Baker will be good police, and Bunk concurs.
- Alliterative Name: Brian Baker.
- Almighty Janitor: McNulty encourages him to look at the rank of patrolman as this, as patrol doesn't have supervisors breathing down their back while on duty and thus have a lot of leeway in their interactions with the public, at least for as long as the other patrolmen will cover for them. This includes refusing to do busy work sent down by police brass in favor of catching actual criminals, as Jimmy and Baker do together.
- By-the-Book Cop
- Just Following Orders: Why he initially goes along with the police brass ordering patrol to crack down on quality of life offenses, including ticketing every illegally parked car in the city. McNulty sets him straight and gives him a few new things to think about.McNulty: [Seeing Baker writing up a ticket on a parked car] What's the violation?
Baker: Parking in a bus stop, expired registration.
McNulty: First class police work there, Baker.
Baker: Yeah, well, this is the word we got from up on high. Straight from the 8th floor downtown. I know you think it's bullshit, but I spend my shift where they tell me.
McNulty: Baker, let me tell you a little secret. A patrolling officer on his beat is the one true dictatorship in America. We can lock a guy up on a humble, lock him up for real, or say "Fuck it, let's pull under the expressway and drink ourselves to death", and our side partners will cover it. So no one... and I mean no one tells us how to waste our shift.
- Naïve Newcomer
- No Sense of Direction: Downplayed. He might actually have a decent sense of direction for all we know, (only so many people can tell which compass point they're facing in an enclosed environment) but Colvin doesn't accept his patrolmen being anything less than Scarily Competent Trackers, so Baker gets the fun of carrying around a compass until he knows which direction he's facing and where he is at all times.