Lord Magluis started life as a Jedi foundling. He was acknowledged throughout the galaxy as a very powerful Jedi and also a highly ranked asset to keeping the galaxy in order. Magluis attained the rank of Jedi Master when he was only 18 and sat on the council at 20.
Whilst on a mission to the outer-rim territories, Magluis encountered something very strange and extremely power with the force, the oldest ever Sith holocron. Magluis had only ever heard of the Sith, but had never encountered anything to do with them. For all he knew they were extinct.
The second he touched it, it lit up and from within, an ancient Sith Lord was released; Adas. Adas had a vast knowledge of the force and whilst being trapped within a holocron had learnt everything he could about it. Adas tainted the Jedi and turned him into an agent of evil, the first Sith Lord for 500 years.
Afterthat fateful day, Magluis took on the role as Sith Lord and opened a small academy where he snatched children to be his agents. he did not let anyone become as powerful as he by attaining the rank of Dark Lord.
In the year 1055 ABY, he took on a new aprentice, Kaadan Kresh. 12 years after that, a converted Jedi sprung into the scene, Alegras. He taught them both for a few more years until handing them both over to one of his apprentices.