[Spoilers ahead for Marvel comics and Being Human]
A series’ heart is its characters—whether it’s comedy, tragedy, fantasy, what have you, generally speaking, if you’re going to really capture the audience what you want is a good cast. You could have the most banal or wacky concept in the world, but if you have good characters people like and are interested in, people will watch it. Similarly, you could have the coolest and most fascinating backdrop ever, but without good characters to form that human connection, nothing’s going to glue. So, once you’ve got this band of characters that forms the bridge of audience attachment, you’d be silly to change them, right? Well, not always. Not every series revolves around the same set of fictional people for its entirety, and sometimes it’s beautiful and sometimes it’s bad.
Some series cling to their characters for decades, some change them every few seasons as a matter of course (like Skins), some bring back beloved concepts with new faces (Star Trek: Next Gen perhaps). Every long-running series has a kind of conceptual mould at its heart (e.g. Madoka Magica’s mould is “young girls fight monsters and discover the evil in the system they’re fighting for”) and a set of main characters (Madoka, Homura, Sayaka and co.). Sometimes, if they run long enough, these can get a little tired, so you have to change things up, unless you’ve got something truly episodic with no excessive continuity like old sitcoms. Generally, you can either change the characters (for example, bring in a new group of Magical Girls to follow) or break the mould (now instead of this being a story about fighting monsters it’s about fighting each other and their various dubious motivations).
Comics often keep their moulds, but get new characters within it. The new Thor comics star a woman (to the ecstatic cries of one half of the internet and the groans of the other, of course) not because Thor as we know him has been warped into a sex change, but because a new character has picked up the hammer and gained the powers therein, thus becoming the person to carry the title. So you can still have all your adventures that play with the universe and themes that suit that story, but to keep things fresh there’s a new lead to follow, get attached to, come to understand. It keeps the flavour and formula the same, but changes up the human connection to make things interesting and fresh. Thor was also a frog at one point, I’m pretty sure, so it’s not as if this is something new. Continue reading