I think Red John is a Dr.Jekyll/Mr Hyde character who on the surface is a well respected, calm, charismatic individual. Underneath, his shadow side is a demented, serial killer.
Bret Stiles is dying ( I believe this a symbolic death) He's been fighting his shadow self and it's killing him. Red John is emerging.
Bret Stiles is powerful, enigmatic, manipulative and has limitless resources and brain washed followers. As a cult leader he's the ideal villain.

He's a schizophrenic mastermind lunatic and a fabulous actor!  And quite possibly Patrick Jane's biological daddy.