Murders by Niko Bellic

There are many hit missions in Grand Theft Auto IV, and Niko Bellic has accrued the greatest body count of any GTA protagonist thus far. Here is a list of his intended targets ("collateral" murders such as those of unidentified gunmen, pedestrians, or police are not included):

Murders

Kalem and Bledar Morina – They are the first murders by Niko in Liberty City. Niko murdered the two in the defense of Roman Bellic.
Dardan Petrela - Murdered for assaulting Roman Bellic.
Vladimir Glebov - Niko shoots him in the eye for sleeping with Mallorie Bardas.
Lenny Petrovic - Murdered on orders of Mikhail Faustin.
Jason Michaels - Murdered on Faustin's order for "messing around" with Faustin's daughter.
Lyle Rivas - Chased and killed on orders of Bruce Kibbutz.
Mikhail Faustin - Murdered on orders of Dimitri Rascalov, and to appease Kenny Petrovic.
Tom Rivas - Murdered for not paying off his debt to Bruce Kibbutz.
Jayvon Simson - Murdered for ratting on Dwayne Forge.
Charlie - Murdered for having attempted to arrest Niko Bellic, Trey Stewart and Johnny Klebitz.
Tom Goldberg - Murdered for giving Francis McReary potential legal trouble.
Marlon Bridges - Murdered on Trey Stewart's orders.
Trunchez Brothers - Murdered so that Dwayne Forge can get the Triangle Club back.
Oleg Minkov - Murdered on orders of The United Liberty Paper
Teddy Benavidez - Murdered for failing to pay Ray Boccino.
Kim Young-Guk - Murdered on Jon Gravelli's orders.
Aiden O'Malley - Murdered for trying to testify against Derrick McReary.
Bucky Sligo - Murdered on Derrick McReary's orders for threatening the McReary family.
Anthony Spoleto - Murdered on Gerald McReary's orders, to sour the relationship between the Ancelotti crime family and the Albanian mob (who were framed for the killing).
Frank Garone - See above.
Charles Matteo - Murdered for discovering Phil Bell's role in sabotaging a cocaine deal between the the Ancelotti crime family and the Russian Mafia.
Jim Fitzgerald - Murdered after causing trouble for Ray Boccino
Isaac Roth - Murdered for threatening Ray Boccino.
Luca Silvestri - Murdered for stealing diamonds from Ray Boccino.
Joseph DiLeo - Murdered in a shootout with Niko Bellic.
John Barbosa - Murdered in a shootout with Niko Bellic.
Ray Boccino - Murdered for being a potential rat on James Pegorino's orders.
Anthony Corrado - Murdered for leaking information to the FIB via wire, for James Pegorino.
Dimitri Rascalov - Murdered for betraying and trying to kill Niko.

Random Encounter Kills

Eddie Low - Murdered by Niko in self-defense (Eddie Low is a random character, so killing him or even encountering him in the first place is optional).
Clarence Little - Can be spared, although in a later random encounter, he must be killed anyway, unless the encounter is avoided altogether.

Choices

Jimmy - Niko can kill him during the mission Clean Getaway. It would change the dialogue with Vlad through the phone.
Ivan Bytchkov - Niko can let him fall from the building, on Vlad's orders, or help him up.
Cherise Glover - Niko can shoot her in Ruff Rider, or let her live.
Clarence Little - Niko can kill him, on Francis McReary's orders, or let him live.
Alonzo - Niko can kill him, or let him warn Teddy.
Adam Dimayev - Niko can kill on orders of The United Liberty Paper or just leave.
Darko Brevic - Niko can either take revenge by shooting him multiple times, or spare him.
Unnamed Jewish Mobster - Niko can kill him in the Majestic Hotel or walk away.
Vasily - Niko can kill him in a drive-by in the mission Wrong is Right
Sergei - In the Deal storyline, Sergei attempts to kill Niko, but kills Roman instead; Niko kills him in revenge.
James Pegorino - In the Revenge storyline, he is killed for killing Kate McReary.

Kill One or the Other

Trey "Playboy X" Stewart or Dwayne Forge - Both characters ask Niko to kill the other.
Francis McReary or Derrick McReary - Niko can shoot either with his sniper rifle; again, both have asked Niko to kill their opposite number.