That boy is Mark Ruffalo

Mark Ruffalo is an American actor who needs to be in a good movie soon (and fast!). You can see him dancing in underwear in the movie Eternal Sunshine of the Spotless Mind. Meanwhile check some shirtless photos of him here; 1, 2 and 3. Luckily, he is also hot in clothes; 1, 2, 3, 4 and 5.