There are some special skins in Borderlands 2 for the PC, PS3, and Xbox 360, called Veteran Skins that are given to long time fans of the series.
Technically you don’t really need to be a long term fan, you just need to have played the original game at least once.
To unlock the Veteran Skins for Borderlands 2, you simply need to have a saved game from the original Borderlands saved onto your system somewhere. I’m guessing it might need to be in the same location as your Borderlands 2 saved game.
You don’t need to beat the game or anything, you just need to have any saved game.