Sidekicks interest me. They’re such a staple of fiction, whether it’s the companion who’s cleverer than the hero, some mild comic relief or an excuse for someone to get beaten up and kidnapped on a regular basis. Where would the Lord of the Rings be without Sam? Blackadder without Baldric? Granny Weatherwax without Nanny Ogg? The right sidekick in the right place can totally transform a character.
I think there are probably a few things to remember. The first is who your hero is. The thing with sidekicks is that they seem funny and brilliant right up to the point where you decide to give them real attention, whereupon it usually turns out that they don’t have enough to sustain the novel. Or they steal so much of the scene from the main character that we all stop caring.
One big question is ‘what does this secondary character tell us about the main one?’ More specifically, what does the way the main one behaves in the relationship tell us about that main character? Going back to Pratchett’s Esme Weatherwax, we learn quite a lot about her from her constant bickering with Nanny Ogg, not least because Gytha Ogg is the one who sees through her best, having known her for years.
In a lot of ways, the sidekick is a lens through which we see an otherwise difficult character. Think of what Watson did for Holmes, serving as a device to let us into a mind that might otherwise have seemed too alien in its brilliance. Or the way Doctor Who’s companions provide a human insight into situations, allowing the Doctor to work in his own odd ways.
The real trick with a sidekick is to do that without sacrificing their own identity as a character. One easy way to achieve that is to give them either a fractionally different take on a central issue, or to have them less totally absorbed. Let them be the one who has family, and normal hobbies, and friends, while the hero is the totally obsessed one. It’s just one way of doing things, but it has possibilities.