Culture: It's as if Shatner never existed...

The summer blockbuster season officially kicked off on Friday with the worldwide release of Star Trek. Uncharitable souls are calling it Star Trek XI, underlining just how dependent the Hollywood studios are on sequels to herd people into the multiplexes. Strictly speaking, though, it isn't a sequel – it's an attempt to "reboot" the franchise by pretending the previous 10 Star Trek films haven't been made.

The reboot formula was patented by Christopher Nolan with Batman Begins (2005). As with Star Trek, the marketing for that film emphasised that it would be an exploration of the central character's origins – his psychological back story. This proved successful enough to spawn a genuine sequel, The Dark Knight (2008), which became the biggest blockbuster of last year. Superman Returns (2006), which ignored this formula in favour of a straight retread, was less successful. At this stage, a sequel looks unlikely.

The precise definition of a reboot is elusive. Clearly, having a new, younger actor play the central character is essential, but if that were the only criterion, then On Her Majesty's Secret Service (1969) would have been a reboot when, in fact, it was just another film in the continuing series. On the other hand, Casino Royale (2006) is generally regarded as a reboot of the Bond franchise – though, confusingly, it was also a remake. As with Batman Begins, the key point is that it explored the character's origins.

What of Terminator Salvation, another of this summer's blockbusters? Is that a reboot of the Terminator franchise? The answer is no – it is a sequel. Confusingly, though, it is a sequel to Terminator 2, not Terminator 3, which the film-makers are pretending never happened. In that regard, it is more like one of those sequels that comes around after a very long gap – like Live Free or Die Hard (2007), the fourth in the Bruce Willis-fronted series, which appeared 12 years after the third, Die Hard: With a Vengeance (1995).

So far, reboots have largely proved successful, with one glaring exception. After the first Hulk (2003) failed to pull in the crowds, an attempt was made to relaunch the franchise with The Incredible Hulk (2008). That, too, proved a box-office disappointment. Apparently, there are some comic-book characters audiences just aren't interested in, no matter how fascinating their origins.