Pretty much everyone knows the story behind the Green Lantern: each member of the Corps is given a powerful ring that is limited in ability only by the willpower of its user. The more creative and determined you are, the deadlier the results will be. For this game, Snowblind tapped John Stewart, a prominent GL from the late '80s and the recent cartoon.
Stewart, unlike other, more artsy Lanterns, tends to use his ring in more straightforward ways - in this case, it's a giant sledgehammer. Hitting a gorilla. Later in the game, when you've powered up your characters, you'll see some better uses of the ring's potential.