Boy
As you guess it right, the boy is the protagonist or the main helper in those free online games. Some of them are only conditionally about boys, as it is sometimes impossible to say that a hero of some of them is really the one in the classical understanding of this notion. Like it is in the ‘Zombie Bike Adventure’, where the main acting hero would be one if he weren’t a dead rider on a bone bike.

Some of them are for boys, not about them. And these are shooters, riders, and racers. Surely. What else would one expect from boys games? However, have a huge fun playing them!