"Why are they starting the 'Spider-Man' movies over?"
It's a question we've heard echoed again and again (and again) by casual movie fans who have recently seen the trailer for The Amazing Spider-Man; those still wondering why, what should've been the fourth film in a popular movie franchise, is now a film with an all new cast, an all-new look, but is essentially the same origin story that was covered by director Sam Raimi and Co. in the 2002 Spider-Man.
Comic book fanboys and/or hardcore cinephiles can probably explain the situation - but to those still looking for answers, today we have a rundown that will help explain what is going on with this Spider-Man movie situation, and give you some information that will make you sound like the smarty in the group, when the subject inevitably comes up in social discourse.
Comic Book Retcons
Properly referred to as "retroactive continuity," 'retconning' is when comic book creators go back and revise aspects of a character or story that have been previously established in continuity. See, comic books are a unique medium in that they've run for an incredibly long time, but under the guidance of many different creative visionaries. The writer/artist team that created Superman in the '30s had different ideas and sensibilities than the creative team in the '50s, the '80s, and so on; Batman has been around since 1939, and even "newer" superheroes like Spider-Man or the X-Men have been around since the '60s, about half a century (or more). In that time, more than a few writers and/or artists have altered a superhero's backstory, powers, costume, attitude - sometimes even their identity (for example, since 1940 four different boys have taken on the mantle of Batman's sidekick, Robin).
On the one hand, the constant change of creative teams keeps a comic book character fresh, as new people bring new ideas to the table, and keep the character relevant and connected to the (at that time) current generation. On the other hand, there is the danger that a prior idea may become outdated, unsustainable over a longer course of storytelling, or was simply born of an era and/or social context that no longer exists. When that happens, comic book creators rely on 'retcons' to right (and re-write) the (possibly) outdated aspects.
In 2000, Marvel Comics launched their "Ultimate Marvel" comic book universe, starting with Ultimate X-Men and Ultimate Spider-Man. The goal was simple: create an alternate reality in which popular superhero origin stories were re-told in a modern context - free from decades of convoluted and dated backstory. New readers could start from a fresh beginning and follow a character through a more familiar world; longtime readers could get a new take on their favorite heroes, but could still enjoy the "classic version" being offered by the original comics.
As you may surmise, a modernized look at Marvel superheroes also became the basis for a fair number of superhero films - including the upcoming Avengers movie, which borrows many elements of the modern "Ultimate" universe - not least of which is a Nick Fury who looks like (and is played by) Sam Jackson. Thanks to a wonderful and dedicated creative team (the same writer has written all 140+ issues of the series), Ultimate Spider-Man's modernized take on the web-slinging superhero became a hit - and the primary inspiration for the franchise reboot film, The Amazing Spider-Man.