If it would count, I say SSB. I heard about it before, but only because I knew that Sonic was in it, other than that I knew nothing about it. One day, my friend told me about it, and I acknowledged that I knew about him, and it was then it happened.......he decided to bring over Brawl for us to play. We were trying to unlock Sonic for my sake, but we never got around to that. However, I did end up having a blast even though I onlyplayed Mario when I was able to. The only other times is when I was forced into a Kirby battle (yeah, don't ask :p), and when my friend made me use Pit against my will (which was ironic, as he is now my favorite smasher), as well as various other instances in the SSE when mario was unplayable. It has been over a year since I played it last, but now I have way more characters that I liked.
If you mean stand-alone series, then I got competition with Fire Emblem and Kid Icarus Uprising (though i ever played the latter) both which were introduced to me by SSB4. I was onto the latter, after I was captivated by Pit's new moveset, as well as himself as a character. The FE story is a bit longer. I heard of FE as Ike was one of my friends favorite smashers, as well as the first one I have seen him use. I think what got me into fire emblem was the inclusion of Robin and Lucina. I had no interest in either of them as characters, but I was a bit curious about. I read more about the game and thought this is the fantasy game I have been looking for. Later, I started watching other people play FE on youtube, and found it very cool. Later, I found a hacked version of Fire emblem 8 and 7 for my tablet. You do the rest of the math.
Wooh, my thumbs hurt. (:p no not really)