I guess I ought to
I'm an Australian student, aged 17, who's been writing fanfiction since I was 11 and imagining it for much longer. Back then, I didn't know it was fanfiction.
I created my first OC in 1999, when I first met internet fandom by typing '+"Star Wars" +fan' into a search engine. Yep, she was a shocking Mary Sue. I originally created her because the situation I wanted to write in needed extra characters. After all, in Star Wars there are new worlds and new characters all the time.
When I came to HP fandom just after the release of Goblet of Fire, I didn't even last through the writing of one fic without creating an OC. My first HP fic was published in Spetember 2000, and it featured no less than 3 OCs. I had already come up with an idea for an MWPP-era fanfic. And, despite what some people may try to do with their fanfics, you need OCs to write in the MWPP era, because we simply do not have enough canon characters to populate Hogwarts at that time.
However, when I truly fell into the realm of OC reading and writing was when I was confronted by a Slytherin boy, Head Boy, cousin to the Malfoys, and hating it. He wanted a one-shot story, so I gave him one. Then he wanted a longer story, so I agreed. Now he has demanded that I write, at very least, a trilogy starring him. So, he became the OC-protagonist of my fic Dux Dolosus (RATED R). He quotes Shakespeare and he drives me absolutely crazy. Pelase tell me I'm not the only person whose OCs drive them nuts.
It's great to meet you, everyone, and I look forward to discussing OCs with you! *Ponders sff_corgi's post*
Yours in fanfiction,