Antagonist

Antagonists, or simply enemies, are the main villains of the Grand Theft Auto games. The antagonist of a GTA game is usually a person that has betrayed or hurt the protagonist on a personal and social level, and spends the game moving against the protagonist in multiple ways.

Description of Most Antagonists

In the GTA games, the main antagonist is introduced at the very beginning of the game, but as a ally or friend. Sometimes, the antagonist is the main reason that a protagonist visits the city/state. In most GTA games with antagonists, they usually fake a friendship or business relationship with the protagonist then suddenly, in one mission, reveal their hate for the main character and begin to open fire on them with a weapon. The main character always hunts down and eliminates the antagonist eventually.

Antagonists usually have a gang behind them for protection. The main character will battle the antagonist group and usually take them over.

Grand Theft Auto III

Catalina

Antagonist Group: Columbian Cartel
Killed in: The Exchange
Reason: Shot down by a Rocket Launcher by Claude.

Salvatore Leone

Antagonist Group: Leone Family
Note: Salvatore provided work for Claude and eventually sold him out to the Colombian Cartel, however Claude manages to escape.
Killed in: Sayonara Salvatore
Reason: Shot by Claude.

Grand Theft Auto: Vice City

Sonny Forelli

Antagonist Group: Forelli Family
Killed in: Keep Your Friends Close
Reason: Shot dead by Tommy Vercetti

Lance Vance

Antagonist Group: Vance Crime Family
Killed in: Keep Your Friends Close
Reason: Shot dead at the rooftop by Tommy Vercetti

Grand Theft Auto: San Andreas

Frank Tenpenny

Antagonist Group: Tenpenny is/was a member of the Community Resources Against Street Hoodlums, otherwise abbreviated as C.R.A.S.H., who is working out of Los Santos, San Andreas.
Killed in: End of the Line
Reason: Crashed in the heart of Ganton and succumbs to his injuries.

Big Smoke

Antagonist Group: Ballas and Los Santos Vagos
Note: Big Smoke is the top lieutenant in the Grove Street Families but he betrayed the gang and he worked with Tenpenny and Pulaski, along with the Ballas.
Killed in: End of the Line
Reason: Killed in a showdown by CJ.

Grand Theft Auto: Liberty City Stories

Massimo Torini

Antagonist Group: Sicilian Mafia
Killed in: The Sicilian Gambit
Reason: Shot Down by Toni.

Grand Theft Auto: Vice City Stories

Jerry Martinez

Antagonist Group: Similar to Tenpenny, Martinez is a corrupt Sergeant for the United States Army and is not in any gang. He does however have control over some gangsters in Vice City that try to kill protagonist Vic Vance, but they are not an official gang.
Killed in: Last Stand
Reason: Killed by Vic.

Diego and Armando Mendez

Antagonist Group: Mendez Cartel
Notes: The Mendezes are the powerful drug cartels in Vice City. However, they want all businesses of Vic and knock Vic and Lance out but all their efforts fail to kill the Vance Brothers.
Killed in: Light My Pyre and Last Stand, respectively.
Reason: Killed by Vic.

Grand Theft Auto IV

Dimitri Rascalov

Antagonist Group: Russian Mafia
Killed In: A Dish Served Cold (Revenge)   or A Revenger's Tragedy (Deal)

Reason: Killed by Niko for betraying him and trying to kill him and his cousin.

Jimmy Pegorino

Antagonist Group:  Pegorino Family

Killed In: Out of Commission (Revenge)  or A Revenger's Tragedy (Deal)

Reason: Killed by Niko for killing Kate McReary, or killed by Dimitri Rascalov.

Darko Brevic

Antagonist Group: None

Can be killed in: That Special Someone

Reason: Can be killed by Niko Bellic for betraying him, Florian Cravic and the rest of the fifteen men who were killed back in the war. Though he can be spared.

Grand Theft Auto IV: The Lost and Damned

Billy Grey

Antagonist Group: Was the President of The Lost Brotherhood before being arrested. He is now at the Alderney State Correctional Facility, which is protected by the LCPD.

Killed In: Get Lost

Reason: For attempting to rat out Johnny Klebitz  and Angus Martin and pretty much the rest of the club.

Ray Boccino

Antagonist Group: Pegorino Family 
Killed In: Pest Control GTA IV.
Reason: Tried to control the Lost Brotherhood, was responsible for Jim Fitzgerald's death and convinced Billy Grey to rat out Johnny and Angus.

Notes: He was killed by Niko in GTA IV for Jimmy Pegorino who believed he was ratting out the Family.

Brian Jeremy

Antagonist Group: Brian's Chapter.
Killed In: Bad Standing or Brian Jeremy(Random Encounter). Reason: Killed by Johnny for attempting to kill him, Jim Fitzgerald, Terry Thorpe, Clay Simons and some loyal bikers to Johnny's side.

Grand Theft Auto: Chinatown Wars

Wu Lee

Antagonist Group: Lee Family
Killed in: Salt In The Wound
Reason: Killed by Huang.

Grand Theft Auto: The Ballad of Gay Tony

Rodislav Bulgarin

Antagonist Group: Russian Mafia.
Killed in: Departure Time
Reason: Killed by Luis for trying to kill him and Anthony "Gay Tony" Prince.

Timur

Antagonist Group: Russian Mafia.

Killed in: Departure Time

Reason: Killed by Luis for trying to kill him and  Anthony "Gay Tony" Prince.

Notes: Right-hand man of Rodislav Bulgarin

Rocco Pelosi

Antagonist Group: Ancelotti Family.
Killed In: Departure Time (Possibly).
Reason: Ripping off Gay Tony, intimidating Luis into trying to kill Tony and associating himself with Bulgarin.