Yes, I know this is stealing Wind's idea..
But he'll forgive me.
#1: BILLY GREY:
In early 2008, Billy was arrested with heroin and placed in rehab. Johnny became president in his place, giving Billy's motorcycle to the Angels of Death as a peace offering.
Johnny has worked hard to make peace with THE ANGELS OF DEATH.
And within only five minutes after his return, Billy has broke the troche, and restarted the war.
So, yeah, that's why their mentioned to be fighting in the other two games.
In the TBoGT mission Chinese Takeout, it is revealed that Billy was making a deal with a Triad leader — he would lead Johnny Klebitz and Jim Fitzgerald to the Triad building, and would let the Triads exterminate them and take the Heroin for themselves (he also has a brief, 2-line conversation with Luis Lopez and Gay Tony in this mission). However, when the plan came to come in the mission This Shit's Cursed, Johnny and Jim, despite losing the Heroin, were able to escape the ambush. Not only that, but Billy also ended up arrested by the LCPD (possibly tipped off by the Triads). This left Johnny Klebitz in charge of The Lost. This started a brief civil war between Brian's Faction, which culminated in Johnny killing Brian.
In the mission Was It Worth It?, Ray Boccino commented that Billy told him that Johnny and Jim were backstabbers. Also, Agent Jones, an unseen FIB agent, told Johnny in his second phone call to him that Billy was testifying against him. In the game's final mission, after Thomas Stubbs explained that Billy was going testify against the MC, Johnny decided to take the last combat-enabled members of The Lost MC (including Terry Thorpe and Clay Simons) and mass-attack the Alderney State Correctional Facility. After blasting through all the security guards, Terry and Clay head back to their bikes while Johnny confronts Billy, who killed a security guard. After Billy taunts Johnny about killing him, Johnny is hesitant to shoot Billy. Billy lunges at Johnny with a knife, before Johnny finally shoots and kills Billy..
#2: BRIAN JEREMY:
Brian Jeremy was a 39-year old acting-Lieutenant of The Lost MC and was known to be fiercely loyal to the gang's incarcerated leader, Billy Grey. He is apparently displeased with the direction Johnny Klebitz is taking the gang in due to the truce with The Angels of Death. Brian constantly argues with Klebitz over Grey, and always defends Grey, even if he is making the wrong decisions. Johnny also constantly insults him, specifically his combat skills among other things.
Brian (along with Johnny, Terry, Clay, Jason and Jim) were the 6 bikers who visited Grey to pick him up from jail in the game's intro. He later appeared assisting the game in the missions Angels in America and It's War; in those cutscenes, he was seen quarreling with Johnny. Brian also backed up Billy and the gang during Billy's mass raid on the Angels of Death Clubhouse, and likely agreed with his decision to steal and keep the heroin—despite Johnny's claim that this would provoke too massive a scale of a war between the Heroin's original owners (the Algonquin Triads) and the AOD, Brian then (off-screen) physically took possession of the heroin, and then gave it to Johnny during an unsuccessful drug deal; however, despite having backup, the deal failed.
In the TBoGT mission Chinese Takeout, Billy Grey was seen organizing a betrayal plot against Klebitz and Fitzgerald—this would take place in the mission This Shit's Cursed. Billy and Brian would stand outside the Algonquin Triads building and allow Johnny and Jim to walk into the building, and let the Triads take their Heroin in exchange for Johnny and Jim's murders. However, in what may have been a police setup by the Triads, the police arrested Billy—Brian's attitude and words after his arrest implicate that he almost certainly is completely unaware that this was a setup by Billy, thus leaving him convinced that Johnny betrayed him.
After disappearing, Brian created a faction of The Lost (the Jeremy Biker Gang). When he and his gang were confronted by Johnny's faction in End of Chapter, Brian revealed his traitorous nature—convinced that Billy's arrest was Johnny's fault, he sent his faction to (unsuccessfully) attack Johnny, Jim, Terry and Clay. Brian escaped, but considering the very large amount of hitmen who attacked, it appears as if Brian convinced many members of The Lost (in a brief time span) to join his side.
Ray Boccino, who The Lost had met before, was allied with Jeremy; but not desiring the civil feud between the factions for his business with The Lost, Boccino betrayed Jeremy in Bad Standing and exposed his location to Johnny, who went and confronted Brian at his house. Johnny can either kill him here, or spare him and then later kill him after he betrayed him a second time in a Random Encounter.
Were he obviously hasn't learned his lesson, and leads you into an ambush..
Someone who betrays their best friends, always deserves to be killed in a empty basketball court..
#5: CLEARENCE LITTLE:
The fact most people take pity on him, and spare him, makes it real douchy of him to later return and try killing you..
#6: RAY BULGARIN:
Probably one of the most evil characters of the GTA series. Aside from his whole human smuggling past, his chronic disorder and his generally nasty, aggressive personality, his appearance in TBOGT makes him one of the most horrible villains in the series. While he may appear affably evil or even somewhat petty and harmless at first (in stark contrast to his brief appearances in the main game), he soon gets several moments: the brutal murder of the cook and his subsequent betrayal of Luis, and his cruel treatment of his sister, even shooting at and possibly killing her..
#7: DIMITRI RASCALOV:
We ALL hate this guy.
Like Ray, he is probably one of the most evil GTA characters of the entire series.
At first, he seems like a pretty nice guy.
But after Niko kills Lenny Petrovic, the son of the country's most powerful Russian mobster Kenny Petrovic, because Mikhail has a vague, unfounded suspicion that Lenny is a snitch. Dimitri tries to reason with Mikhail, saying Lenny Petrovic is dating his cousin and that law enforcement doesn't need a snitch to keep tabs on them due to Mikhail's methods, but to no avail.
Later, Dimitri meets with Niko privately, claiming that Kenny Petrovic would spare them both if Niko were to kill Mikhail. It's possible that Dimitri lied, but Niko seems to have never gotten any trouble from Petrovic as promised. When Niko was supposed to collect his payment, Dimitri revealed that he was allied with Ray Bulgarin, who employed Niko as a human trafficker across the Adriatic Sea until he blamed him for a sinking ship. Niko escaped with the aid of his friend "Little" Jacob Hughes, but failed to kill Dimitri and Bulgarin—both would continue to pursue Niko from then on. The same day, his cousin Roman's apartment building and taxi depot were burned down.
Soon after betraying Niko, Dimitri became a major figure in the Russian Mafia and started his own cocaine importation operation. He was arrested but released for attempting to bring cocaine into Liberty City along with a business associate. After they went into hiding in Bohan, he discovered that Roman still frequented a gambling den in Broker. Dimitri was owed an unspecified amount of money from The Lost Brotherhood associate Ashley Butler and used this to his advantage, sending two henchmen to her place, and convincing Lost MC Vice President Johnny Klebitz, and a member of the Uptown Riders, Malc, to kidnap Roman to try to lure Niko to his death, but Niko successfully rescued his cousin and Johnny was left in the dark as to why he had to execute the kidnapping.
In the next month or so, Dimitri allied himself with Italian mob boss Giovanni Ancelotti, becoming their cocaine supplier and to profit from his family's rackets. The Pegorino Family learn of this affiliation and decide to steal a shipment of cocaine in Catch the Wave. His first action was to extort deputy mayor Bryce Dawkins to help them control several construction unions, blackmailing him with knowledge of his gay affair with Bernie Crane. Coincidentally, Niko was an old friend of Bernie's and stopped the blackmailers. He also tried to ambush Bernie and Niko by boat while they were having lunch. Niko then allied himself with Gambetti family boss Jon Gravelli and destroyed their shipment of cocaine.
At the end of the game, Dimitri offered to sell the heroin from Jimmy Pegorino to a third party; Pegorino had Niko working for him at the time. Pegorino was made aware of their feud (which started when Rascalov sold Niko out to Ray Bulgarin, continued when he burned their Broker Safehouse down, and then finally crossed the line when Rascalov kidnapped Roman); but Pegorino still asked Niko to participate in the deal. The player is then given the choice of whether Niko will participate in the deal and be paid, or rebel and kill Dimitri. Dimitri is killed by Niko in either scenario..
#8: AMANDA DE SANTA:
Amanda was working as a stripper and possibly a prostitute (according to Trevor and as implied by her son) when she first met Michael Townley.
At Michael's first mission.
Amanda cheats on him with her teenis coach, causing Michael to bring down an entire house.
#9: TRACY DE SANTA:
Tracey's true personality is hard to define, as she is quite upset about many things in-game, including having bad relationships with the members of her family, who disapprove of her behavior. She appears to be very spoiled and immature, and is portrayed as a stereotypical "daddy's girl". She is known to be rebellious in her actions against her parents, and even going as far as auditioning for Fame or Shame without their approval.
Tracey is also shown to be quite naive and dim-witted, often fitting the role of a stereotypical dumb blonde. Her dialogue is almost always used for comic relief. Her sheep-like nature gives her the impression that everyone, including those outside of her family, has her own best interests in mind. When things do not go according to her standards, she is usually rendered shocked and throws a temper tantrum, usually screaming and pounding her fists on the floor, blaming everyone that is "ruining her life"..
#10: DOCTOR FREDLANDER:
Dr. Friedlander is portrayed as an over-the-top version of a Hollywood psychotherapist. He is overpriced (as seen in an email where he raises his rates by a "reasonable" 75%) and does not appear to care much about his patients and their problems. During Michael's therapy sessions, he is seen looking at his watch waiting for the session time to expire. He appears unconcerned about Michael's behavior as the latter confesses that he is able to kill without remorse.
Dr. Friedlander also appears in the mission Reuniting the Family in which he listens to Amanda and Michael argue about their relationship, but he makes no effort to intervene in any way.
Later in the game (in an optional visit), he tells Michael that he has gained his own TV show and will be leaving Los Santos. He then informs Michael that he needs to find a new therapist and implies that he is going to use Michael's case in his show. Angered by this, Michael chases after Friedlander. Michael then has the choice to kill him or let him go..