Morales was born and raised in Brooklyn, New York City, the then-13-year-old son of an African American father and a Puerto Rican mother. Axel Alonso has described Miles as an intelligent nerd with an aptitude for science similar to his predecessor Peter Parker.
 
Contrasting Miles with Peter Parker, Bendis has depicted different conflicts and anxieties for the character. Right after acquiring his superhuman abilities from a spider bite at the home of his uncle, Aaron, whom Miles admires but he does not initially know is a career criminal, Miles' father, Jefferson, explains to Miles that before Miles was born, Jefferson and Aaron were thieves who spent time in prison, and that while Jefferson reformed when he got older, Aaron has not.