With two different series about zombies walking the earth, Robert Kirkman may be perceived as having crossed the line with too much zombie material, if such a thing is possible. However, the creator feels that Fear the Walking Dead is an important and useful addition for Walking Dead fans. It allows them to go back and fill in the complete story in a way that the main series will never do. It answers questions and provides backstory in a way that would now be awkward for the original show to contextualize.
When The Walking Dead began, Rick Grimes, the series' main character, woke up from a coma. The outbreak that led to the mass infection and the creation of "walkers" had already happened, civilization had already collapsed. Fear the Walking Dead, which is currently on hiatus for its second season, tells the story from the beginning. This frustrates many fans, as the characters are reacting in very different ways than the ones they are already familiar with. However, Walking Dead creator Robert Kirkman told the crowd at the Fear the Walking Dead panel at San Diego Comic-Con, that this is exactly what he loves about the show.
In The Walking Dead, everybody already understands what's been going on, but we have to assume there was a time when they did not. Everybody who lived through the initial outbreak, or was at least conscious for it, didn't automatically assume "zombies," because that would be insane. Let's be honest, if there was an actual zombie outbreak in the world, most of us would not jump to that conclusion first. Odds are it would be an actual virus of some kind and the first guy that jumped to the conclusion of a zombie outbreak would end up in prison, or possibly a mental institution.
While the audience of Fear the Walking Dead has all the information that the original show has given us, the characters don't. Besides, which is truly scarier, being attacked by a walker when you're armed and ready for them, or not even knowing what in the hell the thing coming at you really is?
Taken together, Fear the Walking Dead and The Walking Dead itself will paint a complete picture of the apocalypse, from infection to, well, wherever The Walking Dead concludes. Fear the Walking Dead begins the second half of their second season August 21. The Walking Dead will begin Season 7 in October.