I have two, and I'll admit, they are both kinda lame, but I'm being honest:
- The guy who beat my in my 1st MMA match. I was an ignorant guy, who said shit like "I don't do SPORT jiujitsu, I do MMA!!" and won my first match, and then got destroyed by a purple belt in my 2nd. He checked my ego for me (big time checked it), and led me to seek out more grappling instruction (I did Muay Thai for 10 years before 1st MMA fight, and almost no true grappling). I haven't fought MMA again, due to getting addicted to BJJ. Him humiliating me was the best thing that ever happened to me in martial arts honestly. It made me know how much I didn't know.
- The second...Frank Mir. I know...hes not the most liked guy in the world. I've never met him either. But, when I started, I was a bigger guy (6'2 / 220) and thought the jiujitsu stuff was just for small guys. Then..I saw the videos of Mir submitting guys, and him submitting two monsters with foot/leg locks (Tank and Brock). He kinda convinced me of big-guy jiujitsu working.
So there it is. Its lame. But that's what sparked my love for BJJ.