There are two levels on which you can view the minor characters in The Stranger, including Marie (the lover), Old Salamano (the neighbor), and Thomas Perez (the foil). One level is that they are all characters that drive the plot forward.
On another level, these characters help to illustrate the principles of existentialism, or the absurdity of our lives in which we know life is finite and meaningless yet we must pursue a meaningful life anyway.
Marie is the lover and someone who potentially could reveal feelings in Meursault. She functions as a foil (a literary device to reflect, like tin foil, traits in another character) to Meursault, by showing herself not only as sensual but as emotional. He, on the other hand, lacks emotional depth and only interacts with her superficially, physically and sexually.
Old Salamano is an old man, who seeks to give Meursault advice, but ultimately is in no position to advise anyone. He has a dog who goes everywhere with him as a constant companion and even...
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