"We're going to see this through to the bitter end. Or... lager end. "
The leader of the group, who assembles his school friends in order to complete a failed bar crawl from their youth, thus setting the events of the movie in motion. While charismatic and persuasive, he's hedonistic and irresponsible, and unlike the rest of his friends never outgrew his teenage mentality.
The Alcoholic: Everyone else sees how harmful his binge drinking is, although he sees it all as a bit of fun and seems to be in denial. Gary is still in the teenage mindset of alcohol making you an adult. He's stopped drinking by the end of the film.
The Alleged Car: "the Beast", which he bought from Peter some 20 years ago.
Attention Deficit... Ooh, Shiny!: has a short attention span and a "selective memory", forgets details of his friends' lives, is dismissive of danger and generally seems very out of it. This is partly because he's a Jerkass and partly because he's an addict, and a suicidal one at that.
Badass: He takes on many blanks and becomes a professional wandering badass by the end of the film.
Blood Knight: Seems to enjoy fighting the blanks the most, egging Steven and Andy on at certain points. He's also the most aggressive other than Andy when dealing with the blanks. He gets into a rumble at the very end of the film, seemingly enjoying himself too.
Deconstruction: He's basically one of the Man Child characters of Spaced, Shaun of the Dead etc. taken to the point where his hedonistic refusal to grow up a bit has long since stopped being charming and has become a bit pathetic and disturbing.
Despair Speech: his monologue to Andy close to the end of the movie, when he states that all his hopes of a better life after high school never came to fruition, reveals the real reason for the bar crawl (i.e. a Bungled Suicide attempt), and says that he's jealous of Andy for having a perfect life.
Destructive Saviour: he saves humanity from the Network's domination, but plunges Earth back into the Middle Ages in the process.
Determinator: he's really single-minded when it comes to completing the pub crawl, managing to drink even during a fight.
Driven to Suicide: Gary attempted to commit suicide at some point before the film due to his disillusionment over how the high school pub crawl seemed to be the only high point in his life.
Dye Hard: he's been regularly dying his hair black for over twenty years, but his stubble and eyebrows give his natural hair color away.
Fingerless Gloves: Wears sleeves over his hands that keep his fingers bare to achieve this effect. Conveniently enough, they also serve to hide the bandages from his suicide attempt.
The Friend Nobody Likes: He's inconsiderate and selfish, and his friends find him irritating and pitiful. In a very atypical Earn Your Happy Ending, he becomes a steadfast, loyal friend to the young robot versions of his gang, thus finding his purpose in life.
Foreshadowing: When telling Andy of his plan to begin the crawl again, 12 pints from 12 pubs, Andy points out how ludicrously unhealthy this is. It's possible Gary intends to kill himself with alcohol poisoning.
Sad Clown: Gary is obviously not entirely happy, although he does his best to show otherwise.
Scars Are Forever: Has one from when he fell off the stage in his younger years and dislocated his arm. He opts not to show them when asked for proof that he's him, as that would reveal his bandages.
School Idol: As far as he believes, anyway, although he was shown to be reasonably popular with the girls back in the day.
Sesquipedalian Loquaciousness: "Tonight, we will be partaking of a liquid repast as we wind our way up the golden mile commencing with an inaugural tankard in the First Post, then on to the Old Familiar..."
Unreliable Narrator: in the beginning sequence. His later experiences in the town and the way his friends react to him would seem to suggest that he wasn't quite the untouchably cool king-of-the-town beloved by all he remembers himself to be, or at least that what was cool in the past isn't now.
Foil: he's a serious, responsible, married teetotaler - that is, a complete opposite of Gary.
Genius Bruiser: Rugby player and also a lawyer. Even when hammered, he's one of the few to notice Oliver's birth mark re-appearing, and he also provides some very good arguments that the Network cannot refute, as any good lawyer should.
Happily Married: Or so he claims. He's actually been having major difficulties as of late, although they get resolved by the apocalypse.
Gary's friend, the only one to show any enthusiasm about the bar crawl. A fitness fanatic with a successful career in architectural consulting, he has a failed marriage behind him. Also, he's been in love with Sam Chamberlain since their teenage years.
I Will Only Slow You Down: Offers this when he's caught by the Blanks. Subverted: he actually manages to slip them, making him a rare example of someone who will Only Slow You Down managing to eventually catch up again.
The Lancer: Despite being friends, he's a bit of a rival to Gary. (His last name, "Prince" to Gary's "King", also hints at this status within the group).
May-December Romance: at the start of the movie, he's in a relationship with a 26-year-old fitness instructor. He dumps her after the events of the movie and gets together with Sam instead.
Spoiled Sweet: He comes from a very rich family, yet is the most soft-spoken of the five guys.
Played By: Rosamund Pike
"If you think I'm going to have sex with you in the ladies, you're crazy!"
Oliver's younger sister, who crosses paths with the group during their pub crawl. She's the object of affection for both Gary and Steven; the former slept with her during their teenage years.
All Girls Want Bad Boys: She'd been there as a teenager, but by this point she's outgrown that mentality, probably because of being left behind that night. While she admits that she doesn't exactly look back on their fling without fondness, nowadays she just can't look at Gary as boyfriend material anymore.
Affably Evil / Faux Affably Evil: Genuinely somewhere between the two. It wants a genuinely better universe and will reward those who volunteer generously. On the other hand, refuse and your arse is grass. Literally. You'll be mulched into compost.
Omniscient Morality License: Deconstructed. It serves mainly to piss humans off about him being high and mighty, to the point where Gary and the vast majority of humanity eventually tell him to buzz off and accept a societal breakdown so he can leave us alone.
Affably Evil: Genuinely polite and friendly to the gang, buying them all a round of drinks and asking that they address him as "Guy" instead of "Mister Shepherd". Even after he gets his head smashed by Andy, he's willing to buy another round and have another polite chat.
What Happened to the Mouse?: No details as to what happened to him come up in the epilogue. It's not even that easy to see him in the crowd of Blanks that leave the ruins of Newton Haven. Granted, he didn't have a huge role until after he got replaced, but still...