Jean Gabin did not receive an Oscar nomination for portraying Jacques Lantier in The Human Beast.
Jean Gabin plays the train engineer who we first meet just doing his job, and tries his best to run his train which he lovingly refers to it by name. Gabin in these early scenes gives a man who seems to just be doing his job, and enjoying it for the most part. The normalcy of this man seems to change though when we see Lantier away from his train and meeting with a woman. Gabin is outstanding in this scene as he opens it up showing Lantier as a genuine romantic, but something quite strange happens when instead of trying to kiss her he tries to strangle her instead revealing that there is something quite wrong with Lantier.
Lantier though is not a psychopath in the usual fashion rather he has bouts of madness caused by what he describes as bad blood. What makes the scene all the more disconcerting though is Gabin's portrayal of the madness. He is entirely genuine as he begins to romance the woman, but when the madness takes him Gabin shows it as something primeval. There is nothing of the normal unassuming Lantier when he tries to strangle but rather a beast that appears from. Gabin does well to not over do this moment instead he makes it feel entirely natural, which in a way makes it far more chilling. From this point on in the film it is hard to look at Lantier quite the same way.
Gabin understands the set up for the character and for the rest of the film presents Lantier as a ticking time bomb. Gabin is very effective in creating this fearful symmetry as he still plays Lantier as a mostly quiet man, who seems just not to want trouble more than anything, yet behind it we now there is something evil that can come from him. Gabin is very good in that he does threaten with the beast in the man, but he does create a certain intensity in his performance. It is not an intensity of a man repressing evil, but instead he suggests a man who always has a constant fear in his thoughts for the moment when the madness takes over which may come at any time for any reason.
Lantier quickly finds himself in a difficult situation when he falls in love with a woman named Severine (Simone Simon) who has far too many affairs with far too many men which results in a murder. Only Lantier could connect her with the crime, but he does not do to his attraction. Gabin is again very authentic here as he portrays Lantier love for this woman, who is in fact very manipulative of him. Gabin does not put on a big show for this romance, but rather keeps Lantier properly as he always been which is a humble soul. Gabin is quite poignant because there is no false presumptions in his characterization of Lantier, the love is always something Lantier truly feels.
This love gets him nowhere though as Severine only encourages the madness when she tries to convince him to murder another one of her lovers. Gabin is again brilliant in his portrayal of the madness take hold although this time he does not have the power or the will to stop himself from doing something horrible. The murder scene is quite a brutal one. This is not due to what is being shown but rather seeing this usually fairly gentle man become this monster. That would mean nothing as well though if Gabin was not entirely convincing in this descent into insanity. His transformation is sudden but realized by Gabin as visceral attack from the man's second nature.
Gabin's performance does not really create an character arc in the traditional sense, but the is the genius of his performance. Lantier's tale of woe is made powerful by this dynamic that Gabin keeps to which is that of the entirely decent man, who can become a horrible creature not from his own will, but that of something beyond his control. Gabin even keeps to this even at the end as Lantier understands that he has murdered someone. His reactions is not of more madness, but rather Gabin showing Lantier returning to his humble self who unfortunately cannot bear the guilt and the grief involved with his actions. This is moving portrait of Gabin as he allows to really feel the painful struggle of this man whose own mind is his own worst enemy.