Today is pretty straightforward: it's a Rebel trooper! These guys fight for the Rebel Alliance. The helmet is long because it is meant to protect the neck.
Alas, there are no weapons for this Rebel trooper.
Lego Rebel trooper:
He's apparently happy about something. I'm not sure what that could be, since he doesn't even have a blaster.
Episode IV Rebel trooper:
See Wookieepedia for more information on the Rebel trooper.
See Bricklink for parts information for today's build.