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From Wikipedia
The New York term hero is first attested in 1937. The name is sometimes credited to the New York Herald Tribune food writer Clementine Paddleford in the 1930s, but there is no good evidence for this. It is also sometimes claimed that it is related to the gyro, but this is unlikely as the gyrowas unknown in the United States until the 1960s, according to some sources.
"Hero" remains the prevailing New York City term for most sandwiches on an oblong roll with a generally Italian flavor, in addition to the original described above. Pizzeria menus often include eggplant parmigiana, chicken parmigiana, and meatball heros, each served with sauce.
From its origins with the Italian American labor force in the Northeastern United States, the sub began to show up on menus of local pizzerias. As time went on and popularity grew, small restaurants, called hoagie shops and sub shops, that specialized in the sandwich began to open. By the late 20th century, due to the rise of large franchisee chain restaurants and fast food, the sandwich became available worldwide. Many outlets offer non-traditional ingredient combinations.