The film starts off with a rich landlord's attempt to evict a lot of poor people from a low-income apartment building that he owns, and they rebel against him, threatening him with violence should he go through with the eviction. There is a great scene where we see the landlord's wife showing him that in order to calm down all those people, all that he has to do is get rid of the strong ones that keep starting the trouble. There's a great bit of symbolism here as she cuts the heads off the tallest of the flowers in her flowerpot, leaving only the crowd of smaller, weaker ones. Take out the strong ones, and the rest will subordinate.
Thus the movie does not set out dealing very directly with the unenviable role in relationships that women played in the 1950s, not under Franco in Spain, but in the Mexican society in which Bunuel lived at this point in his career. Instead, the movie makes a more specific comment on the state of the union as a whole, as is suggested in the line to Don Andres (the rich landlord who is throwing all of his poor tenants into the street), `Thank you, Don Andres. You're the pride of a country without people.'
At this point in the movie, one begins to try to make ties between Don Andres and Franco, Spain's oppressive dictator at the time the film was made (and also the reason that the movie could not have been made in Spain in 1952). Franco is something of a rich and oppressive landlord himself, although the movie does not spend much time on the idea of an all-powerful and enormously wealthy landowner.
As was the case in A Woman Without Love, the Brute very soon goes into the story of a woman who is constantly brought suffering by the men in her life, even if only indirectly. The movie starts off making a strong comment about the suffering of many at the hands of a small elite, and then it quickly explores an individual situation within the population. These are a typical group of poor people, and their efforts to prevent themselves from being thrown on the street and, more importantly, the efforts of their landlord to evict them, provide the conflict focused on in the rest of the film.
Don Andres hires a huge man from the slaughterhouse, a man who adores him since he has been a mentor for his entire life, and the man he hires is determined to strike fear into the hearts of anyone who would dare to stand against this wonderful man. There is a lot going on here that deals with superficial impressions, since Pedro, the Brute (played by Pedro Armendáriz, who, as an unfortunate side note, committed suicide in 1963), is completely determined to help Don Andres but then changes his mind entirely once he gets close to the people that he is sent out to scare into submission.
Pedro is a brute of a man, hence the title of the movie, but he faces the reality of what he is doing when he becomes close to the daughter of the man that he accidentally killed under his assignment from Don Andres. This bit of irony is the confliction of the martial law enforced by the powerful elite as it conflicts with the larger population, the humanity of which is too often overlooked. He was determined at the beginning to set the troublemakers straight, but it is not until he is forced to take shelter among them that he realizes who the real troublemakers are (`I may have done something wrong but I didn't know you then.').
It would seem that this portion of the film presents the harshness of an authoritarian regime as misdirected and even naïve rather than inherently evil, although it is equally likely (and, indeed, probably more so) that it is a message to those very regimes (specifically that of Franco) of the reality of their form of government. Brute is a strongman for the rich elite and then ends up getting help from them and even falling in love with one of them, at which point he changes his mind, no longer wanting Don Andres to have his way and for all of these people to be evicted. He has, in effect, been separated from his brutish side by his intermingling with the very people that he was sent out to oppress.
There is a great scene during the chase, by the way, that I just have to mention. At one point, when Pedro is running through the alleyways, there is a shot of him running in one direction, and his shadow, through trick lighting, clearly runs in a completely different direction, going down a different alleyway. At this point in the movie, Pedro separates from his darker side, turning toward helping the poor people that are being evicted. Just a little bit of trick lighting (a VERY common technique in black and white filmmaking) that really stood out to me.