Cosmo Entelecheia
Cosmo Entelecheia is a mysterious group that wants to destroy the Magic World for unknown purposes. Twenty years before the series, its leader the "Mage of the Beginning" or the "Life Maker", a very tall man, clad in black robes and cloaks with an empty hood, was the mastermind behind the destruction of the Magic World. He easily manages to wipe out Ala Rubra, though Nagi is eventually able to defeat him. The group later reemerges under the leadership of Fate, or at least, it seems so. In the later chapters it is revealed that Dynamis is their current leader.
Read more about this topic: List Of Negima! Magister Negi Magi Characters