Creating a character for a comic doesn't need to be hard, and it doesn't matter where the primary inspiration for the character comes from. There are some things to look out for though…

I'm focusing on design and creation of major characters here. You will find that often minor characters can break a number of the rules I lay down here and still work.
So, to begin, the concept. If your character is meant to fit in with a cast who are already in the comic, or are taken from a series (if it's a fancomic or spin-off) or in a situation where you've already designed some characters, you must consider how your character will fit in with the rest of the group.
It's easy to fall into the trap of creating an entire cast of heroes who are the kind of characters you like…

….However, this approach soon leads to problems when nobody can tell your characters apart, nobody becomes attached to a particular character, and the characters don't have anything to talk about. If you put two stoic badass characters in a room together, they'll probably stand in either corner glaring at each other, which doesn't really give much room for interesting dialogue.
Try to vary your cast so that they all have reasons to like or dislike each other, and some ground for conflict.
Even characters who have the same goal, like say, a party of adventurers searching for a lost city…Let's just make some up…

The characters have ended up together because of a common goal, but between them, they all have personal motivations and feelings at work. They don't need to be as simple and cliched as the bunch I just made up. A character's reasons for liking or disliking another character could be multiple and nuanced.


Your character's place in the world is important to consider. Be wary of whimsical characters who don't fit with the setting…

If it's an intentional comic device, or the entire comic is full of wacky, whimsical stuff, then this kind of things works perfectly. Take ‘Hellboy’ for example, in which we feel totally at ease with a demonic paranormal investigator fighting zombie nazis. As a general guideline, the more serious and realistic your comic is, the less people are willing to suspend disbelief. Once you establish the rules of the world in which your comic is set, people will happily believe characters who fit within these rules. A magician fits in fine in a fantasy setting, and in an over-the-top, hyper-real setting, people will suspend disbelief of things like gigantic manga swords, ridiculous hairstyles and people fighting in high heels and corsets.

So…onto character design. Take your concept and refine it down to simple facts. How old is your character? How tall? What does s/he do? What setting does the character live in?
Here's an example character. He's a space cowboy who lives in a ‘Firefly’/'Star Wars'/'Cowboy Beebop' kind of rough, lived-in sci-fi universe. To make him look weary and sarcastic, I've given him small eyes. The bigger, wider and brighter a character's eyes, the more honest, innocent and open they will tend to look. I've given him an angular, clean shaven face, and neat hair which makes him look young and like he cares for his appearance, the angular look makes him a little edgy and gaunt too, like he's used to missing meals now and again. The neat eyepatch has echoes of ‘pirate’, can tie in as a possible plotpoint and makes an interesting feature. Note down details such as the exact shape of any jewellery, and in this case, the toggles on the coat, how his gun looks and a quick sketch of how he looks from behind.

This much or less is probably the level of detail you should go for in a comic. If you go further, adding more and more bits, you may end up with a character who looks cool, but you WILL regret it when you have to draw them more than once or twice. If you keep forgetting bits of detail or you ‘chibify’ or simplify your character more panels than not, it's often a sign that your design is too complex and needs reconsidering. Leave really complex designs like this for video game designs….

Try drawing your character a few times. If you're not sick of drawing them after that, then you're probably onto a winner.
Good luck and have fun!