Anti-Hero: He's no white hat, but he's still far more moral than Alex initially was and far more considerate of civilian cost. When Roland, a Gentek scientist and one of Alex's Evolved, mocks Heller for thinking he's a hero who is willing to kill thousands to get at him. Heller's response:
Heller: Did I say I was a fucking hero, you piece of shit?!
Appendage Assimilation: Gains new abilities by tearing off and assimilating the limbs of Blacklight Abominations and Evolved with those powers.
Badass Normal: Before his transformation, he fights his way to the middle of the Red Zone alone and kills a Brawler Hunter using only a combat knife.
Batman Gambit: His long-running intimidation scheme for Galloway, which was useful for a while but panned out badly. In the various side-missions, Heller also wraps Blackwatch around his finger with a series of these.
Determinator: His first reaction to seeing Alex Mercer, super-strong super-agile notorious bio-terrorist scourge of New York? Pull out the only weapon he had at the time - a large knife - run up and slit his throat. He then charges Mercer and stabs himself several more times, again without success. Even this did not deter him, and after chasing him across the Red Zone he still tries to stab Mercer, despite knowing it won't work. Alex must need the Super Strength to lift a man with balls that size.
He Who Fights Monsters: Present and invoked deliberately. To have a shot at taking down Mercer, Heller will have to become just as or even more powerful, and equally monstrous, which would be a hell of a feat. Subverted. He does end up stronger than Alex and perhaps even more physically monstrous, but he retains his faith in humanity, and does not kill at least Colonel Rooks because he loves his family.
Hopeless With Tech: Apparent in Mission 3, where he has troubles even reading the keyboard and doesn't bother logging off the computer he was using.
While the keyboard did have a "triangle" key, and was thus no conventional computer, one gets the feeling that Heller's had similar experiences in the past.
Manipulative Bastard: Much like Mercer, Heller plays hail-Mary with Blackwatch command structure, and especially their field commander Rooks. Presumably, his own military experience facilitated his expertise with which he infiltrates Blackwatch. Likewise, he was able to milk Galloway for information for a long time, though that backfired badly when he stretched it too far.
Papa Wolf: The sheer amount of hatred directed at Mercer as a result is truly frightening to behold.
"Enough of your fucking weird, fucking rambling SHIT. GIVE ME MY DAUGHTER!"
Person of Mass Destruction: Fully capable of destroying everything in the streets of New York in somewhere between an instant and a few minutes, by himself.
Plague Master: An even better example of one than his progenitor, as he can infect his victims with a particularly vicious power named Biobomb. The afflicted are first engulfed in a mass of fleshy tentacles, then they are torn apart by the tentacles, which then proceed to impale unfortunate bystanders. He can also summon and control up to four Brawlers (depending on Mass upgrades).
Scary Black Man: Considering his powers, which become even greater than Alex's, they don't come much scarier.
Combat Tentacles: To an even more extreme degree than Mercer, apparently. His Tendril powers can be used in conjunction with Wreaking Havok, allowing for wholesale devastation of scenery as well as large numbers of Mooks.
Sir Swears-a-Lot: Becomes noticeably much more vulgar after he loses his family.
Smarter Than You Look: He's gruff as all hell and not always eloquent, which makes him seem a bit like Dumb Muscle. However, he's at times startlingly witty (though he ascribes to Black Comedy) and the way he utterly turns Blackwatch upside-down makes it clear that he's tactically brilliant. Likewise, being a sergeant in the Marine corps requires no little amount of intelligence.
Spanner in the Works: Unwittingly at first, and then later intentionally, screws up Alex Mercer's plans to take over the world.
What You Are in the Dark: Decides not to kill Rooks when he is on the phone and only they are in the room because he sees how he does care for his family, and doesn't want to turn out as bad as Mercer.
Father Luis Guerra
A priest who runs the church in the Yellow Zone that Heller and his family once attended. He tried to meddle with Blackwatch's experiments, but failed and barricaded himself in his church. Heller snaps him out of his Despair Event Horizon and Guerra provides him with intel on Blackwatch supplied by a contact called Athena. Alex Mercer and a horde of Infected kill him after Heller becomes a threat to his plans.
Badass Preacher: He's as compassionate as any priest should be, which does not mean he's averse to keeping an iron pipe close at hand should someone threaten his flock.
Dark and Troubled Past: The guy knows a lot more than he should oughta about guerrilla warfare. Apparently, he's had a lot of tattoos removed.
The lead virologist of Gentek, he's also in charge of its major projects in New York. Because Heller was infected directly by Alex Mercer, Koenig has taken a particular interest in him. He is one of Mercer's spies, having been infected with the same strand of Blacklight that gave him and Heller their powers, and was in charge of developing Whitelight- an upgraded version of Blacklight.
Mad Scientist: Pretty much a given, especially with the track record of other Gentek scientists. He is elated when he sees Heller is infected but alive - such an intriguing subject! Being an Evolved, he has other motives for investigating Heller.
Manipulative Bastard: Plays Heller like a fiddle for a few missions, much like Karen Parker did to Mercer in the first game.
Meaningful Name: König (of which Koenig is an alternate spelling) means "king" in German. He's the head virologist of Gentek.
The Chief Financial Officer of Gentek, Galloway is in charge of Gentek's financial affairs. She is also one of Alex Mercer's spies, having been infected with the same strand of Blacklight that gave him and Heller their powers.
Femme Fatale: She tends to rely on sex-appeal in order to get her way.
Heel-Face Revolving Door: Works for Mercer, being a spy in Gentek, but then helps Heller against Mercer's Evolved. Finally shifts back to Mercer's side when Heller doesn't take her offer to leave the city with her.
Dirty Business: He's not a very good person, at one point sanctioning rape since to do otherwise would waste man-power and supplies. However, the game leaves him a somewhat sympathetic figure and surprisingly the Lesser of Two Evils, without denouncing his underlying mission of sterilization and control.