The Graviton Particles are special particles of gravity itself. It's discoverer and user is Dr. Franklin Hall A.K.A. Graviton as Nick Fury called him.
Ten years ago, when Franklin Hall joined S.H.I.E.L.D. on a project to recreate the Super Soldier Serum, he discovered the Graviton Particles and contained it in the reactor inside the Helicarrier.
As the reactor had gone critical, Fury ordered Hall to shut it down, but instead, he set the reactor to maximun causing it to explode, which bombarded him with the particles he discovered.
After gaining Gravikinesis powers, he was intending to use it on Fury but was knocked out locked up in The Raft for ten years until the Breakout.
As he woke up, he used his newfound powers against all those who stands in his way, which are the Avengers, but was defeated by all five founding Avengers.