Dark Angels
The Dark Angels have the proud honour of being the first of the Space Marine legions from the days when the Emperor still walked among his people. However they hold a dark secret in that during the time of the Horus Heresy and the great betrayal, half of their number sided with the traitors. 10,000 years later, keeping this closely guarded secret is one of their main drives, as they obsessively track down any trace of their fallen kin, many of whom have now formed Chaos Space Marine warbands.