This is a very interesting issue to consider, because actually, although Geraldo is the real focus of this fragment from The House on Mango Street by Sandra Cisneros, I believe that Marin is the true protagonist of this tale. Let us remember what the definition of a protagonist is. A protagonist is the main character we focus our attention on and the person who sets the plot in motion. If we think about this definition for one moment, the person who sets the plot in motion is Marin as she reports her answers to the police about her brief meeting with Geraldo:
She met him at a dance. Pretty too, and young. Said he worked in a restaurant, but she can't remember which one. Geraldo. That's all. Green pants and Saturday shirt. Geraldo. That's what he told her.
Geraldo is a character that we never meet and are only described through Marin's limited knowledge of him. It is as if the narrative itself is hiding him from us, just as he had to keep himself hidden. We only see him through Marin's eyes and we are told very little about him. The fragment instead explores the impact of his death on Marin, and her reflections on the life of migrant workers such as Geraldo. This is why I believe that Marin is actually the main character or protagonist in this fragment.