Darth Bane is EU. The one created the Rule of Two. I think this was more of an extension on why there were only Darth Vader and the Emperor from the movies.
Again Darth Maul's apprenticeship was stated in the EU.
It has been suggested that Darth Maul, Count Dooku and General Grevious represent aspects of Darth Vader. Maul as the young apprentice and hitman. Dooku as the trained Jedi turned Sith with twisted ideals. General Grevious for the mechanical nature of Vader.
Maul was suggested as a stop-gap for the time being until something better came along.







