Think of a hero, any hero. From a book, from a film, anywhere. Get them clear in your head, see them standing in front of you. Now look past them - do you see anything at their side? It may not be very clear, but you might make it out - a face, perhaps, or just a smile, the glimmer of eyes, perhaps just a fleeting shadow. That is, if you're not already distracted by someone else lurking over the hero's shoulder, grinning at you in a way that says "Yup, me too!"
Congratulations. Meet the sidekick.
Of course, they're not always called that. Sometimes they're a family member - half-brothers, long-lost parents and other forms of estranged relative are quite popular - or a mentor or guide of some sort, perhaps a guardian if our hero at the stage where they could logically fight off a serious foe by themselves. Other times they're a close friend or sweetheart who refuses to be left behind, or maybe an new acquaintance picked up along the way in some exceptional circumstance, who has decided, hey, this looks like fun, I'll come with you! But, though they come in many shapes, sizes, forms and varying degrees of usefulness, you can be pretty sure that no hero is likely to get through a journey without someone trotting at their shoulders.
Sidekicks are a staple part of most stories and - for the most part - they're pretty cool to have around. They link your main character more firmly to the world they live in, as well as providing the much needed realism that humans, by and large, are social creatures who like having friends around to provide practical and emotional support when the going gets tough. Their personalities can either compliment or contrast that of the hero, and the interaction between them is awesome if you want to show, rather than tell, someone's feelings at a given time. If the story's a serious one, sidekicks are frequently called upon to lighten the mood with some form of comic relief, and heck knows they get themselves into enough trouble to shift the plot along nicely - whether it be accidentally starting a bar fight, tripping over the map everyone's spent a chapter and a half looking for, or getting kidnapped by a major villain and spurring any particularly reluctant heroes into action. And, from an authorly perspective, how can anyone resist breaking the readership's heart by killing off a much-loved character at any moment? (I must confess to doing something similar in my Aeserion Trilogy ... my readers were not impressed)
And the best part? They can do all the things that your hero won't / can't / isn't stupid enough to do.
Hero doesn't much fancy climbing the tree to retrive that honeycomb? Send in the sidekick.
When crossing a swamp, hero has found some way to clear the nasty bits, but you need someone to retrieve a neccessary item from the bottom of the swamp? Send in the sidekick.
Hero has half a brain in their head, and knows better than to go and poke the funny glowing object in the middle of the room that will result in the raising of a vast skeleton army defending the only way into the villain's lair? Sorry sidekick, not sure your Life Insurance covers this...
They suffer for their art, bless them.
On the other hand, sidekicks do often suffer from Cardboard Character Syndrome if not used well. How many books have we read where the hero or heroine's "best friend" is nothing but a peppy, brainless idiot who chirps along and believes everything can be solved through the power of Twoo Fwendship, a hug and a cup of hot chocolate. Just as bad are the sardonic background lurkers who are meant to be "cool" and funny with their wry senses of humour, but just end up as those people who say unneccessarily depressing things in an attempt to look witty. For perfect examples of rubbish sidekicks, read the House of Night series by P.C. and Kristin Cast. I'm pretty sure Fred and George, Elladan and Elrohir and all the other famous sets of twins out there would grind their heads into the wall at the two horrors we are supposed to find endearing.
Thankfully, however, most well-written books will have used their sidekicks as they should be - another interesting character to encourage the reader into the story, strap them in, and hand over the barf bag when things get hairy. That is, if they're not sitting at the front going "it's way more fun if you put your hands in the air, trust me! Wheee!" or, alternatively, hiding under your seat whimpering, "goodbye, cruel world!"
And now, just to finish it off, in an ode to the thousands of poor unappreciated sidekicks who have trekked through the ages beside all the lost kings, freedom fighters and Chosen Ones of a thousand tales, I give you...
Ten Awful Things Sidekicks ALWAYS Have To Do.
1) When your hero is injured in battle, you will have to rescue them, putting your own neck on the line in the process. Most likely sustaining some sort of injury to yourself in the process.
2) When your hero falls into some sort of trap, you will have to get them out again. Even if there are snakes involved.
3) When the villain comes after your hero, you will probably be kidnapped and interrogated for information. You may also be placed in a precarious position and used as bait to lure your friend into the villain's trap.
4) When the author wants to create an atmosphere of complete desolation and hopelessness, you will most likely be horribly wounded and die an agonising death in the hero's arms. They will not stop shaking you and yelling at you to come back. You will not have the strength to slap them and tell them to shut up and let you die.
5) When the hero is in one of their angsty moods, you will be sent in to try and cheer them up. And you will probably lose a few teeth in the process.
6) When the hero recovers from said angsty fit, you will have to listen as they start up a grand speech about the neccessity of their quest, and their determination to complete it whatever the cost. For the fifty-thousandth time.
7) When your hero is locked in the battle with the arch-villain / chasing the murderer across the rooftops / finding the final clue to the mystery, you will be left behind to fend off the hordes of minions / gangsters / well-intending but misguided authorities that will try and stop you.
8) When your hero is exhausted, you will have to carry everything so they can rest. That is, if you don't end up carrying them too.
9) When your hero meets the woman / man / creature of indefinite gender of their dreams, you will have to watch their heartfelt moments together. Fifty billion times. While resisting the urge to remind them that the building is about to crash down on their heads.
10) When the battle is won / mystery is solved / curse is lifted etc, you will have to stand back and force a smile while your hero gets all the glory, riches and reward that goes with it. You will then have to ask to sleep on the hero's sofa until someone gets back to you on the fleetingly-mentioned paycheck that you aren't sure is ever going to procure itself.