Well, I should get this out of the way.
My early childhood barely had any fighting game influence. I was more influenced by platformers at the time. Then for some time I was more into arcade racers. I had played a few fighting games from time to time, but never truely invested in them. I think the turning point was when one day I was bored enough to look for fighting flash games. Perhaps it was due to actually having a movelist for once, but I began to enjoy it more than I expected. With this in mind, I got myself MAME and began to try out the real stuff. It was the usual culprits, Marvel vs, Street Fighter and KOF as these were the only ones I really knew about. I wanted to try Guilty Gear but alas, at the time it wasn't available. A few years later, I began to take note of Mugen. I saw a few videos, but while the premise was interesting it didn't seem to fully get me to try it myself. It wasn't until I saw it for myself being played in a con that I convinced myself to try it out for myself. Why do I mention Mugen? Because it gave me a taste of fighters outside of Capcom and SNK(accuracy issues aside). After playing some characters, it got me interested in trying their source games. Mugen introduced me to games like Melty Blood, Eternal Fighter Zero, Akatsuki Blitzkampf and others.
In short, a flash game started my interest and mugen proceeded to amplify it.