"So? Do you see me now? Tell me, what do you see? Hm? You have eyes; what do your eyes see? Yes. That's right, you see a skull face. You see me. This skull is who I am, my mark, my proof of humanity. I have no country, no language, no face - but I haven't lost my skull."
The Bad Guy Wins: It's shown that both he and XOF managed to easily bring MSF down with ease at the end of Ground Zeroes, and all signs indicate that the group didn't face any serious opposition until nearly a decade later in The Phantom Pain.
Bait the Dog: Giving Chico a Walkman after throwing him in the prison initially seems like a nice thing to do for a guy that threw the kid in the brig. However, when Big Boss actually listens to the tape, it's audio from the tortures of Chico and Paz. Not quite the best for comfort music.
Big Bad: Of Ground Zeroes, and presumably The Phantom Pain.
Break Them by Talking: Along with some torture. In fact, almost all of his dialogue in Ground Zeroes is composed of this trope.
The Chessmaster: His plan is to deliver a crushing blow against MSF and pin the blame on Cipher, leading the two to destroy one another. Beyond that, his actual attack on Mother Base is quite complex with many layers and angles to it. But it is also very well planned and executed.
Cursed with Awesome: The sheer damage that he's taken inhibits any sort of pain directed at him. Of course, this comes with the price of looking like he does.
Dangerously Genre Savvy: Just in case Big Boss found the bomb he put inside Paz's abdomen, he put a second bomb in her vagina for good measure.
Defector from Decadence: He wants to rebel against Cipher, in spite of having previously worked for the organization.
Determined Defeatist: He has lost everything, face included, yet continues for some (currently unknown) reason.
Determinator: As evil and twisted as he is, he has endured a shit ton of stuff, which hasn't slowed him down in the slightest.
Double Reverse Quadruple Agent: He apparently wants to snuff out Cipher and the Patriots in spite of his apparent involvement with both organizations. Mysteriously enough, he also wants to destroy MSF (later the Diamond Dogs) - the private militia that's focused on going toe-to-toe with the mysterious organization.
Early-Bird Cameo: All of Ground Zeroes counts for this - his motivations are only hinted at.
Enemy Mine: Defied. When Paz asks him if he'd kill Zero for her, he bluntly responds "Not for you."
Evil Counterpart: Of Big Boss - both are crack operatives that have a considerable amount of influence over the people that work for them. As Big Boss finds himself Slowly Slipping Into Evil, he becomes the Eviler Counterpart.
Furthermore, both have horrific and tragic pasts, but even when Big Boss fell, he was never completely consumed by the darkness.
Evil Is Hammy: Going by his behavior in the trailers, and his audio logs in Ground Zeroes, he's apparently very fond of dramatic language and gesturing.
Expy: Some fans have drawn a few paralels between Skull Face and The Joker, particularly his incarnation from The Dark Knight and the eponymous Joker graphic novel. That the audio tapes, particularly the one with Skull Face detailing his backstory can be likened to one of Joker's infamous "scar stories" and the fact that he's a Wild Card playing against both Big Boss and The Patriots doesn't helps one bit.
Facial Horror: His nose is crooked, he sports a Glasgow smile, and his entire face is one huge disfiguring burn scar.
Meaningful Name: Just look at his face and you'll see that his name fits. He even tells people that that's all that people see in him after his skin was burned off.
Mysterious Past: Other than his rather horrific backstory detailing his life growing up in a weapons factory, we know very little about what led him to becoming an agent for the Patriots or what motivates him to want to seek revenge on Cipher. Most curiously of all he tells Chico "Your Boss (Big Boss) and I go way back." making his career prior to the events of Ground Zeroes even more enigmatic.
Even the backstory we have been given is mysterious. What war was this weapons factory a part of? What nation was this village in? What was his name, his language, his people, or his ethnicity? Your guess is as good as ours is for the time being. The only clue that's given about his country of origin is that he speaks Hungarian at one point - but even that could be something he picked up on as a spy.
"At the infirmary they carried me to, a nurse in the corridor saw me and remarked, as if it happened every day: 'They should let the poor thing die.' Those are the only words of my mother tongue I remember."
Rape Is a Special Kind of Evil: He physically abuses Paz and it is implied that he raped her. It's also heavily implied that he forces Chico to have sex with her so he could play voyeur.
Remember the New Guy: He claims to have gone "way back" with Big Boss, although he hadn't been introduced in any of the games preceding this one.
Revenge: He is apparently out to exact it against the Patriots (including Big Boss, whom he tells Chico that he goes way back with) for an unknown reason.
Ruritania: Skullface can be heard issuing the command "Vigyétek a ketrecébe!" in one of Chico's tapes; the phrase is Hungarian and, since the language is uncommon outside of Europe, it's probable he hails from Hungary or somewhere near the country.
Sadistic Choice: Issues this to Paz. Choose Big Boss or Zero, only one side of the conflict can be saved. Paz ultimately gives away Zero's location.
Shrouded in Myth: His unit, XOF, is evidently shrouded in mystery - even the Marines that were present when he personally visited Camp Omega have no idea who he is or what his unit stands for.
Soft Spoken Sadist: When torturing people one-on-one, he often talks politely while putting them through pain.
Straw Nihilist: He believes in the concept of hope... But only because, in his eyes, almost all hope is based upon superficial qualities, but it helps him survive.
Torture Technician: Counting the audio logs, the only scene where he isn't heard torturing anyone is the opening sequence - and even then, he casually mentions that he tortured Paz.
Used to Be a Sweet Kid: He implies that he was a perfectly normal kid before his village was bombed and he was scarred.
What the Hell Is That Accent?: His voice and accent are different depending on his interrogation subject(s). Also there's a scene where he's issuing orders to soldiers in a softer tone of voice, and then when he's done he switches back to his usual gravely tone. Of course, he might be doing this deliberately.
Where he's from is not clear. However, he speaks one line in Hungarian, which would imply that could be his country of origin - and, given that there were several bombings in that country during World War II, his backstory would support this.
Well-Intentioned Extremist: If his claims of seeking "liberation" are true. It would appear that he's out to get away from Cipher's influence and defeat Zero, and that perhaps he is another villain in a long line of rebellions against the established order set by the Patriots. Since Zero is still "in power" by Metal Gear Solid 4, it seems for him Failure Is the Only Option.
"World of Cardboard" Speech: A villainous variant that is delivered in a post-credits scene (and one of the audio files) - about the song "Here's to You", of all things.
Skull Face: Your favorite song... Nicola, Bart - immigrants wrongly executed... But their deaths served as a message to others: that ours is a society that murders the innocent. Do you, too, believe that your sacrifice will change the world?
Would Hit a Girl: He hits Paz when she objects to his plans, and even strips and belt-whips her, possibly even raping her.
Would Hurt a Child: He has no problem with torturing Chico for information. He even puts screws in his feet to keep him from going anywhere.
Woobie, Destroyer of Worlds: While horrific, Skull Face solely avoids being a Complete Monster for having a horrific past. Listening to him talk about his entire motivation being to make sure his people live on through him, and his words of Nihilistic view on hope, which is the only reason he keeps on living will at least make you feel sorry for him.
Worthy Opponent: Seems to hold Big Boss in high regard, telling Chico he knows Big Boss is going to rescue Chico, regardless of him knowing it's a trap, because he knows Big Boss is a good man. He also quotes him on a number of occasions.
The pilot that assists Snake throughout Ground Zeroes, and the only back-up that he receives for the various operations he carries out in Camp Omega.
Big Damn Heroes: Is the go-to method of extraction for most missions. Notable examples include "Intel Operative Rescue," where he and Snake provide air support while the operative (Hideo Kojima) makes his way to the LZ, and the end of the main story, where he helps evacuate Mother Base during the attack.
Eye Scream/Fingore: Extracting them both will reveal that Glaz is missing his right eye and Palitz has a prosthetic finger.
Foreshadowing: Interrogate either of them, and they will tell you that a "Phantom" is approaching. Whether or not this refers to Skull Face or anyone else is unclear.
Hidden Depths: Should Big Boss knock them out and take them to Mother Base, Miller discovers that they inflicted mutilation upon themselves (Glaz having a glass eye and Palitz having a plastic finger), indicating that even they were remorseful and horrified by what they've done.
Off on a Technicality: While not necessarily free men (negotiations are in progress regarding their extradition for trial), Kaz notes that they're "living comfortably in a loophole," stationed at the secret Cuban blacksite where international law isn't a concern.
Kick the Son of a Bitch: It's pretty telling how much Big Boss and Miller's clients hate these two when you can kill both men and still get an S Rank.
Alternatively, Snake can opt for a non-lethal approach by knocking them out and having them extracted out of the mission area.
Meaningful Name: In addition to the "eye" and "finger" representing their roles as sniper and spotter, Miller says their nicknames are a reference to being "less than human - no heart, just an eye to find their prey and a finger to pull the trigger."
Nonindicative Name: However, their roles as spotter and sniper aren't mutually exclusive - they both alternate between their roles.
Sociopathic Soldier: It's implied that many of their kills were made in violation of international law, and may have included civilians. Kaz notes that their extradition to face trial is a major factor in the ongoing peace negotiations.
Timed Mission: Of a sort. Snake is initially given the approximate location of both targets, but if he takes too long the targets will have moved, forcing him to identify them by face alone.
An undercover MSF operative who has been compromised after recovering a cassette tape relating to XOF. Snake and Morpho rescue him from the base in "Intel Operative Extraction." Turns out to be Hideo Kojima himself.
Ascended Extra: While he isn't important to the story of the game, his role is given a greater significance than the one he had in Peace Walker, where he simply had a cameo.
An American agent planted by the Joint Chiefs of Staff at the Cuban base. Big Boss is hired by his employers to make contact with him and determine the nature of the base's activities. He sets him up to be caught, and must be interrogated to find the real intel.
Deep Cover Agent: He's so devoted to keeping his cover that he asks Big Boss to make their meeting look like an attack, even giving his consent to be choked unconscious.
We Have Your Family: The reason he sets you up, courtesy of Cipher. Boy, the Patriots really love this trope, don't they?
The Mole: One on your side, he's been planted to gather information on the Cuban base, and stashed a tape for you to collect.
Reverse Mole: Then he sets you up, sending you to a trap baited with the wrong tape.
Magical Eye: The E3 2013 trailer features a subtle moment in the character introduction where she gets up from a sniping position and some bruises/shadows around her eyes fade away.
Ms. Fanservice/Stripperiffic: Apparently deconstructed, according to Kojima. He claims that players will "feel ashamed of [their] words & deeds" upon learning the reason why Quiet is exposed like she is.
The Faceless: Almost all of his face is covered with bandages, save his eyes and mouth.
Fantastic Drug: Subverted; he injects Snake with digoxin in an attempt to help him get back on his feet, but it doesn't work as well as he hoped it would, resulting in a Controllable Helplessness scenario for Snake.