What is your main role and how did you pick it?

I've played lol since season 2 and started ranked in season 3. I picked up jungle because Amumu was one of the first champs I really enjoyed, and I stuck w/ it until season 4 changes to the jungle. I sort of drifted through season 4 and started season 5 w/ still nothing I really favored. Then mained mid/top most of this season after picking up Heimer who I hadn't played since his changes (really liked the character when I started but season 2 he was nerfed to not be very good pvp and wasn't a good choice in ranked till his rework), and then switched back to jungle recently bc I got burned out on Heimer.

For me my main role is usually determined by 2 or 3 favorite champs, but I'm sure lots of people have lots of different reasons for what they main so I'm curious what people choose to play and why?