He has mastered a 'formidable' amount of material.
The mountains were a 'formidable' barrier.
a 'formidable' enemy/opponent/weapon
(..) I will lead them in the glorious battle. Battle? Against the meagre might of Earth? Glorious, not lengthy. If your force is as formidable as you claim. You question us? You question him, he who put the sceptre in your hand? Who gave you ancient knowledge and new purpose (..)2012 The Avengers