The concept of parallel universes, or the "multiverse" as it is often called, has come a long way since its supposed inception in the 1950s. It was later popularized by comic books in the 1960s and has since become the go-to plot device for the said piece of literature in case they need to reboot their superheroes. It wasn't until late into the 2000s that the multiverse concept became widely accepted in cinema.