One role the old man plays in "A Very Old Man with Enormous Wings" is to symbolize the thematic issues of the story. For instance, he symbolically represents marginalized people or groups of people. He himself is marginalized because he (1) is alien to the villagers; (2) speaks an unknown language; (3) is old; (4) is ill and apparently disabled; (5) is inexplicable.
Marquez gave this marginalized man enormous wings so that he could be at once repulsive for his insects and uncleanliness and mysteriously great for his wings and angel status. This speaks of how marginalized people in our society seem loathsome and strange and inexplicable, yet have majesty, worth, greatness, power (even though latent), dignity, and potential. In other words, the marginalized have humanity.