In addition to Spider-Man and the Fantastic Four, Marvel began publishing further superhero titles featuring such heroes and antiheroes as the Hulk, Thor, Ant-Man, Iron Man, the X-Men, Daredevil, the Inhumans, Black Panther, Doctor Strange, Captain Marvel and the Silver Surfer, and such memorable antagonists as Doctor Doom, Magneto, Galactus, Loki, the Green Goblin, and Doctor Octopus, all existing in a shared reality known as the Marvel Universe, with locations that mirror real-life cities such as New York, Los Angeles and Chicago. Which two comic book titles were the precursors to the widening of this overall setting?