At its most basic level, Henry: Portrait of a Serial Killer is just that; a portrait of a serial killer, a portrayal of a murderer. In 'Portrait: The Making of 'Henry'', co-writer Richard Fire calls the film "a real week in the life of a sociopath, unadorned by social commentary."
When director/co-writer John McNaughton was given $100,000 by the Ali brothers (Malik B. Ali and Waleed B. Ali), the only mandate they set him was that they wanted a horror movie with plenty of blood in it. McNaughton and Fire quickly decided they weren't going to do a story about a monster or a demon or an alien, but about a flesh and blood man. As McNaughton explains, "The relatively new phenomenon of random serial murder was the core idea for our story because it was more horrific than any fantasy could be. In the end, we know, at least it's doubtful, there are monsters from outer space visiting the earth. Freddy and Jason and those type of demonic horror characters, you know, you can go and have fun at the movies watching these characters do their dirty work, but in the end when you walk outside of the theatre, you know Freddy's not really going to be waiting for you, nor is a monster from Mars, or what have you. But indeed, there could be some stranger lurking out there, looking for a victim [...] Richard Fire and I sort of set ourselves the task of redefining the horror film. Our chief device was removing fantasy, because as long as you have the buffer of fantasy, you have a level of comfort and distance; you know it's not really going to happen, you can enjoy the film for the thrills it gives you, and when you walk out of the theatre, you're safe. The basis of our picture is that when you walk out of the theatre, you feel more threatened than when you walked in" (1999 commentary to UK Full Uncut Edition DVD). McNaughton has also commented, "We tried to do something entirely new, and we came up with a couple of concepts; when you're making a horror film, you often involve monsters, but of course we didn't have the money or the inclination to do some sort of outer space monster movie. However, the character, as based on the true person, is indeed a monster, but also a human being. We also thought we would redefine the horror genre; yes, we were trying to make a horror film, but we're going to make one unlike any other, and go to the root of the idea; a horror film's intent is to horrify, then let's horrify in the extreme" (1999 Interview on UK Full Uncut Edition DVD). As critic Roger Ebert said in his review of the film, "The film uses a slice-of-life approach to create a docudrama of chilling horror. Unlike typical "slasher" movies, "Henry" does not employ humor, campy in-jokes or a colorful anti-hero. Filmed in the gray slush and wet winter nights of Chicago's back alleys, honky-tonk bars and drab apartments, it tells of a drifter who kills strangers, efficiently and without remorse. The movie contains scenes of heartless and shocking violence, committed by characters who seem to lack the ordinary feelings of common humanity. It's justified because of its uncompromising honesty in a world where most horror films cheapen death by trivializing it." ('Henry: Portrait of a Serial Killer Review', Chicago Sun Times, (September 14, 1990); available here).
As such, the film is very much about a monster, it just so happens to be about a monster who is human, one who could very legitimately exist in the real world. In this sense then, the film is about demystification; taking horror in a new direction, returning a sense of realism to the genre, and illustrating to an audience that the evil in humanity can be just as terrifying (perhaps moreso) than the evil of monsters and demons.
However, not only is the film about a flesh and blood man rather than a monster or an alien, but the story is actually told from that man's point of view. It is a film about a serial killer which is told from the serial killer's perspective, rather than from the police's or the victim's, which was how it was usually done up to that time. For example, Thomas Harris' novel Red Dragon, and Michael Mann's film adaptation Manhunter, both of which McNaughton has cited as major influences on Henry, were predominately told from the point of view of the leading FBI agent, Will Graham. And although the killer in both novel and film, Francis Dollarhyde, was characterized to a degree, and whose point of view was presented from time to time, the story was very much Graham's story, not Dollarhyde's. In Henry, Henry is very much the protagonist, it is his story throughout. McNaughton and Fire were not interested in telling the story of how a policeman attempts to catch a murderer (whether he succeeds or fails). Instead, they were more interested in looking at how a murderer goes about his life. As McNaughton argues, Henry is really a character study, as the subtitle, Portrait of a Serial Killer, implies; "Henry, in some odd way, is sympathetic, which is part of the point. In any dramatic story, or film especially, the audience is looking for a sympathetic character, the character it can identify with, and one of the great tricks of the audience in this picture is you come to realize the one you're supposed to feel sympathy for is Henry, and then, by the time you get there, you already know he's a murderer, so it's a very conflicting thing to feel, that moral ambiguity makes the audience feel awkward. This movie very much challenges an audience, their receipt belief" (2005 Commentary to 20th Anniversary Edition DVD)
However, there is more to the film than a character study where the protagonist just so happens to be a killer. One of the other major themes, as McNaughton hints at above in his use of the phrase "receipt belief", is forcing the audience to interrogate itself, particularly its acceptance of, demand for and assimilation of filmic violence. Two scenes are pivotal in this respect, the two scenes which McNaughton argues are the most important scenes in the movie: the murder of the TV salesman (Ray Atherton) and the massacre of the family. McNaughton has spoken at length about these two scenes and their inherent importance in the film, and below are two illustrative quotations where he discusses these key scenes.
The murder of the salesman "is how movie violence is usually practiced: You've got your two heroes, Henry and Otis, and the audience knows who they are by now, they're killers. And you've got this guy who's foolish enough and rude enough to be insulting to them, and you set him up as a despicable character, and this is a normal cinematic way to allow violence. So by the time we get to the murder, the audience is rooting to see him get what he's got coming, and there's a certain amount of humor in the scene, it's played for, not laughs per se, but just to set the audience up in one direction only to reverse the direction later when they see the family slaughtered. This is silly and it's funny, smash a TV over his head; this is how usually violence and mayhem is presented to us, it's deserved by a despicable character so it's okay" (2005 Commentary to 20th Anniversary Edition DVD)
"The scene that disturbs me the most is the scene of the slaughter of the family which they videotape and then later play back for their entertainment, and that's the key scene in the picture and one of the key things the picture is about. We were trying to do something entirely different in terms of the horror film, and in terms of portraying violence, although we were portraying violence. I find that often in horror films and action films, and we did it earlier in Henry, you set up a character as a bad guy, and then you just have this person do all sorts of terrible things to the lead character, or his wife, or his child, or whatever, or a dog, just to show what a horrid person this is. So by the time it comes for this character to get their comeuppance from the hero of the film, the audience is rooting to see this person killed, this person beaten, maimed, because he's got it coming, and it's sort of a purging thing. In the real world, violence has a different face, it's very ugly, and we set up in the early part of the film, here's your typical way violence is portrayed; Henry and Otis go to buy a hot TV because they've kicked theirs in, and the big guy sitting there, Ray Atherton, repeatedly insults these guys. Of course, he doesn't know who they are, but the audience knows who they are; they're murderous killers. So, he's rude, he's abusive, he's insulting, and little by little, you're looking at this guy, and the audience knows. And finally the guy becomes so reprehensible, the audience is saying "Get him Henry, let him have it", and we do this set piece with the TV over the head, and it's violence as entertainment, it's even funny. But it's murder, it's cold blooded, brutal murder. This is violence as entertainment. However, fifteen minutes later, let's have these two guys walk into a home full of completely innocent people, a family, and just brutally slaughter them, and let's shoot it from this little video camera. And then they play it back while they're sitting on their couch, watching it as if it were home entertainment. Something is being said there. And the way it was filmed, you see the setup, then you see the camera, then you start to witness the act, but you're witnessing it on video tape, and you assume you're witnessing it through the eyepiece as it's happening, but then you realize it's not the eyepiece, it's the playback later, and then you see Henry and Otis, and you're there with them watching it, you're participating in watching this and being entertained by it, but it's no longer fun. It's a really, really hideous and repulsive act, and it's a very uncomfortable moment." (1999 Interview on UK Full Uncut Edition DVD)
Taking McNaughton's comments into consideration then, the film is very much about duping the audience; showing them something which they are encouraged to enjoy even though it's barbaric and vile, and then showing them something else barbaric and vile, which they shouldn't be enjoying, but because of the way the scene is shot, that is exactly what they find themselves doing, sitting on the couch with Henry and Otis being entertained by the murder of an innocent family, just as they had been by the comedic murder of an unpleasant salesman. Beyond it's straightforward depiction of a serial killer, the film has a much deeper theme; it forces the audience to interrogate their own desire for violence and their own capacity to view violence as entertainment.