300 isn't a DC comic. It has its own independent creation and doesn't fall under the DC Comics universe. The story and characters are distinct from DC's offerings.
They have had a huge impact. DC Comics' characters have been the basis for countless movies, TV shows, and video games. For example, the Batman movies have been extremely successful and have made the character a global icon. The superhero genre in general, which is so popular today, owes a lot to DC Comics.
DC Comic graphic novels are a major source of inspiration for modern pop culture. They have given birth to some of the most recognizable superheroes in the world. The way they tell stories, with their blend of action, drama, and complex characters, has been adopted by other forms of media. The graphic novels also introduced the idea of superheroes having personal problems and flaws, which is now a common trope in modern superhero stories. This has made the characters more relatable to the audience and has contributed to the ongoing popularity of superhero - themed content in pop culture.
Vampirella wasn't a DC comic. She has her own independent comic series and background separate from DC's universe. DC has its own array of characters and storylines that don't include Vampirella.