Riven is the latest champion to join League of Legends' ever growing army of heroes. She's a very mobile close ranged fighter, with abilities that let her dart forwards in short bursts to harass enemies and get out of trouble. You'll find out everything you need to know in the typically intricate League of Legends hero spotlight video above, which shows how she can be used effectively to chase down enemy heroes. See some screenshots below, showing the three very different appearances provided by her alternative skins.
League of Legends is free to play. You can sign up for an account over on the League of Legends site to get started. League of Legends is on the verge of the huge Dominion update, which will add a whole new game mode, with a brand new map that will encourage faster, deadlier battles for a series of control points. Watch the League of Legends Dominion trailer for an idea of what to expect.