Sneakers is one of my favorite movies.

One of the most interesting aspects of the film is the divergence of the initially similar personalities of Martin and Cosmo due to a life-changing incident, that is, Cosmo’s arrest. Cosmo is even perhaps more compelling of a character than Martin. In a sense, the real Cosmo died the night of his arrest, symbolically at the moment when he kicks and breaks the window as he is being dragged away by the police. The paintings of the Hindenburg that decorate his office are perhaps best seen as a metaphor for how his life came crashing down.
The version of him that survives and is revealed later in the film has been distorted and twisted by his incarceration and by the injustice of only him getting caught and not Martin, who largely put him up to his crime. There are many metaphors in the movie that suggest Cosmo is not a complete person. The sculptures in his office of the silhouettes of a man are another obvious statement to the effect that he is a scarred, hollow man. His office is a very sparse, bleak, and empty: just like his life has been without Martin.
The Cray computer and the sensors that protect the office parallel the intimidating intelligence of Cosmo himself and the emotional defenses he has erected to protect himself from the real world. To defend himself from the type of hurt and pain he has experienced he tries to eliminate (but actually bottles up) his feelings. There is much to support the idea that he himself is aware that this cannot really be done. For example, in the climatic rooftop scene it is clear that Cosmo desperately needs his old friend. We, the viewers, are left somewhat sadly knowing that Cosmo will live the rest of his life without Martin and in despair. One cannot help but wonder how Cosmo would have turned out if he had escaped instead of Martin. How much of our personalites are molded by our life experiences? Can we blaim Cosmo for his point of view if we understand how he developed it?
All of this makes for a compelling character that serves as the bedrock of the story.