Officer Chan Wing-yan
A Hong Kong undercover cop infiltrating Hon Sam's gang.
- Anti-Hero: As an undercover cop, he has to get his hands dirty to keep his cover intact.
- Boom, Headshot!: Courtesy of Billy.
- Dark and Troubled Past: He's an illegitimate son of a triad boss, and he want nothing to do with him. Despite that, this tie almost got Yan expelled from the police academy for real.
- Deadpan Snarker: Especially when paired with Keung.
- Foil: To Ming.
- Good Is Not Nice: He has quite a Hair-Trigger Temper.
- The Hero: The main protagonist of first film.
- Heroic B.S.O.D.: Undergoes one after witnessing Wong's death.
- Jerk with a Heart of Gold: Despite his short temper and being slightly jerky, he truly care and respect the people who are being genuine to him.
- The Mole: He's a mole inside Sam's triad for HKPD.
- Sanity Slippage: Years after years of undercover work got him into several violent streak, which almost earned him a jail time if it wasn't for Wong's bargain.
- Sixth Ranger Traitor: To Sam.
- Surprisingly Sudden Death: Billy shot him while he's backing into the elevator.
- Tragic Hero: Yan spent his life to stay away from the life of crime due to his status as an illegitimate son of a mob boss, he then enrolled in the police academy and was almost expelled due to his background. To stay as a cop, he signed up as an undercover for almost a decade with the risk of being chased by other cops and retributions from rival gangsters along the way in addition to his sanity slippage. Eventually, Yan's opportunity to be officially recognized as a police officer was doomed as he was shot dead by Billy.
- Unperson: Ming erases his police documents after he found out Ming's double identity.
- Weapon of Choice: A Glock 17 pistol.
Senior Inspector Lau Kin-ming
A decorated HKPD inspector, and also a mole for the triads.
- Affably Evil: Noone would guess that he's an undercover gangster, not even his girlfriend, due to his friendly and charismatic behavior.
- Becoming the Mask: His subplot in the first film revolves around this.
- Bitch in Sheep's Clothing: He has an impressive track record to keep himself from being suspected as a mole.
- Character Development: After being a mole for Sam for years and years, Wong's death makes him realize he went too far, so he betrays Sam and decides to start a new life as an honest cop, even though it doesn't turn out like he wanted it to.
- The Chessmaster: On several occasions, especially in the first film.
- Detective Mole: He's tasked to capture the mole within the HKPD, which happens to be himself.
- Dirty Cop: His role as Sam's mole qualifies him as this.
- Driven to Suicide: After he accidentally revealed himself as Sam's mole, he snapped and kills Yeung before gets wounded by Shen. He then attempts suicide by shooting himself through his lower jaw, it doesn't go his way.
- Fate Worse than Death: He shot himself near the end of third film, he survived but he also ended up paralyzed and catatonic due to the injuries the bullet inflicted to his brain.
- Foil: To Yan.
- Hired to Hunt Yourself: Tasked by Wong to hunt down Sam's mole: himself.
- If I Can't Have You...: In the second film he betrays Sam's wife, whom he loves, after she rejects him, which leads to her being killed by Hau's henchmen by being run over with a car.
- My God, What Have I Done?: His reaction to Wong's death.
- Redemption Equals Death: Played with and discussed. Death would have been his redemption on several occasions, him escaping it being his true punishment, suffering Survivor Guilt and slowly going insane. Even when he tries to kill himself, he still doesn't succeed, doesn't die and therefore doesn't reach redemption.
- Redemption Rejection: The result of what's explained above.
- The Starscream: He betrays and kills Sam so he can cover his past and go straight.
- Ungrateful Bastard: To Sam.
- Villainous Breakdown: After he unwittingly outs himself as Sam's mole to his colleagues, since he has already gone insane.
- Sanity Slippage: His character arc in the third film.
- Survivor's Guilt: Undergoes this in the third film after the events he went through in the previous two films.
Hong Kong Police Department
Superintendent Wong Chi-sing
The police superintendent who oversees the Organized Crime and Triad Bureau of HKPD, and Yan's handler.
- Dark and Troubled Past: The second film shows this side of the Wong we get to see in the first one. He set off the murder of high class gangster boss Kwun, resulting into a Roaring Rampage of Revenge by Kwun's son Hau.
- Defiant to the End: A beating by a half dozen of triad members is not enough to make him give up Yan's identity.
- Destination Defenestration: How he was dealt with by Sam's thugs.
- A Father to His Men: He cares about his subordinates, he even sign up Yan for a therapy session to keep him away from jail.
- Heroic Sacrifice: He bought Yan some time for him to escape from the building.
- Oh, Crap!: When Del Piero manages to halt his elevator.
- Reasonable Authority Figure: Exemplified when he gives Yan a chance to remain as a cop after he's about to being expelled from the police academy for lying about his family background.
- Team Dad: To Yan.
The principal of the police academy.
Chief Inspector Luk Kai-cheung
Wong's superior in the police force.
Inspector Lam Kwok-ping
A HKPD CIB inspector and one of Ming's underling.
- Chekhov's Gunman: Despite being a minor character, he played a huge part in shaping the ending of first film and the events of third film.
- Hero Killer: He shot Yan in the head when he's backing into the elevator while holding Ming hostage.
- The Mole: He's one of several moles sent by Sam to infiltrate the police force along with Ming.
- Undying Loyalty: To Ming, even during Ming's confrontation with Yan. Too bad he's just another loose end to Ming.
- You Have Outlived Your Usefulness: After revealing his double identity to Ming, he was killed by Ming and served as the scapegoat to Ming's crimes.
A chubby triad boss and Ming's mentor.
- A Lighter Shade of Black: How Wong sees him initially, compared to his mentor Kwun. Wong even stated he rather see him take charge. However, his treatment of Ngai's surviving family members proved him as Not So Different than other gangsters.
- Affably Evil: When he's in a good mood or when he's with his wife, even more so in the second film during his scenes with Wong.
- Arch-Nemesis: To Wong.
- Bad Boss: He almost got Yan killed twice in the third film. First time he made Yan beat up Shen's younger brother, and second time by put him in charge of a firearms deal with Shen which turns out to be a trap.
- Big Bad: In the first film.
- Broken Pedestal: The events of second film led to Wong's fallout with him.
- Even Evil Has Loved Ones: His wife Mary.
- Even Evil Has Standards: He refused to sell Kwun out to Wong, who made his fortune.
- Genre Savvy: Ming and Billy are not the only moles he sent to infiltrate the police force.
- In the third film, he didn't buy into Shen's persona. Near the end of the film, he even set up an ambush against him.
- Odd Friendship: He and Wong were best friends at one point, he even dined with him at the police station.
- Villainous Breakdown: When the cops converged on him at the parking garage. He tried to call Ming only to find out he's already there, about to tie up the loose ends.
- Villainous Friendship: Keung is his most trusted underling.
Tsui Silly Wai-keung
Sam's most trusted henchman.
- Affably Evil: His light-hearted demeanor is easy to make everyone forget he's a triad member.
- Fake Shemp: He was falsely announced as an undercover cop after his death to keep Yan's cover from being blown.
- Those Two Guys: Keung is usually seen with Del Piero in the first film.
- For the second and third film, Yan shares this role with him.
The youngest son of Ngai Kwun. After his death, Hau succeeded his position as the head of his mob business.
- Affably Evil: He is thoughtful and gets sentimental everytime he talks about his father, whom he respected deeply. His calm and cultured appearance is often underlined by bookshelfs in the background when he is seen.
- Alas, Poor Villain: He was devastated to learn that his half-brother, Yan is an undercover cop as he is succumbing. His action of tucking the radio wires back into Yan's jacket makes his death more tragic, Hau still see Yan as his brother even though he's working against him.
- Boom, Headshot!: Wong shot him in the head while he grabs Sam at the gunpoint.
- Expy: To Michael Corleone. Both of them are the youngest son of their family and succeeded their father's mob business, and they both also have intention to go legitimate. Their personality are also similar to each other.
- Roaring Rampage of Revenge: Goes through this after discovering Wong masterminded his father's murder.
- Even before this, he doesn't shy away from killing (or at least trying to kill) ALL the other triad bosses since he suspects that they all had a role in scheming his father's death.
Dr. Lee Sum-yee
Yan's therapist and later his love interest.
Ming's fiancée, who's a novelist.
- Happily Married: Almost happened with Ming, until she received the recording of Ming and Sam's conversation from Yan.
An enigmatic gang leader from mainland China.