To understand Cottard, but we’ve got to delve a little bit into some old philosophy here, namely that of Søren Kierkegaard, self-proclaimed non-existentialist and also the "father of existentialism." Don’t ask. Anyway Kierkegaard had these notions of societal roles that we all play; if someone asks you who you are, you might say you’re a student, a soccer-player, a daughter, a cousin, a fish-owner, etc. But it’s hard to get under all those roles and see what’s really there, what’s really your essence. The worst part is when we all start conforming to these roles, and to the expectations of what it means to be a student, soccer-player, daughter, cousin, fish-owner, etc., etc.
Yes, we’re getting to Cottard. Cottard seems to suffer from the societal role of "criminal." He doesn’t feel guilt at his crime, whatever it may have been, so much as he is nervous about being caught. He makes friends with people that he thinks may someday serve him well as character witnesses; this need for friends, for security, drives nearly all of his action in The Plague.
Saddest of all is that Cottard falls victim to his own mask of criminality. In fearing his status as a criminal, he becomes one, resorting to smuggling during the plague and a crazy madman postal scene after. Fittingly, he is arrested – the one fear that drove him to action in the first place.
Still, the most interesting aspect of Cottard is his friendship with Tarrou. We already know Tarrou has a soft spot for criminals, but what does Cottard like about him in return? Mostly the fact that Tarrou refrains from judging and offers an ear to listen. We also get most of our information about Cottard from Tarrou’s accounts. We do have to wonder, though, how a man like Tarrou who deals in the black-and-white perspective of plague vs. man can deal with a shade of gray like Cottard. He says himself that he considers Cottard "an accomplice" of the plague.
Yet something about Cottard’s vulnerability, his humanness, draws in Tarrou (and probably us, the reader, as well). Camus, in what seems to be a humanist sentiment, writes Cottard in such a way that we aren’t allowed to cast him off as a senseless criminal. We must see him as Tarrou does: as a man alone and in pain. Perhaps that’s why we first meet him after he has tried to commit suicide; he has our sympathy from the start.