If we don't count the two dorks I'm drawing a comic about right now, my most influential characters are probably Talassa and Gale - I can't pick just one of them, since they're both the main characters of their story.
They were both created on the fly for a 24-Hour Comic in 2010, and I thought that was going to be that - but once I'd finished those 24 pages, I realised I wasn't quite done with them yet, so I kept drawing. And drawing. And drawing. In the end, I'd drawn a 168-page graphic novel about them, and started to build an entire world around them. While I'm done with
them and their story now, the world I built for them is still kicking around, and I've done a few one-shot stories set in it, and I'm considering several longer stories as well.
They're important to me because theirs was the first longer-format comic I ever finished, showing me that I can do this, that I can draw comics properly, that I can tell stories from start to finish. Before them, I almost always got stuck halfway, and found it hard to commit to a story - I always wanted to tinker and change stuff. And while I still do (tinker and change stuff, I mean), I've now gained the ability to push past that and just do.
... Never underestimate the power of finishing things, regardless of quality.