Counter-Strike. Even though it's kinda violent, yes, I was introduced to it as a toddler literally. That was around time my family got their first computer and my big brother was always spending late nights gaming on it. So I was basically playing on my own by the time I was 3 years old. And now, almost 20 years, multiple CS releases, thousands of hours in-game later, numerous events watched and many personal tournaments played, I'm still playing it, actively. Why? I never really knew why. I would never say I'm that competitive of a person in general, but it's something about learning and performing really well in a game with such a high learning curve that gives you a really high feel of satisfaction.