Very little is known about Antonio before the Fall started. He lived either in or near the city of Tijuana. He has an aunt (Elena Reyes) and a brother (Hector). He was involved, to some degree, in gang activity before the outbreak.
After the outbreak began, instead of joining his family at the Rosarito Beach Hotel, Antonio decided to become a member of Los Hermanos Gang, leaving Elena and his brother Hector feeling abandoned and somewhat bitter.