Allied with the Imperial Legion in The Elder Scrolls V: Skyrim? Then do I have an achievement video for you! In order to get the 'Hero of Skyrim' achievement or trophy, you need to capture Solitude or Windhelm, two of the big cities in Skyrim. It all depends on how you're playing through the quest line.
Do that, and you'll earn 30G on Xbox 360, or a silver trophy on PlayStation 3. PC players only get bragging rights. Sorry guys.