He is Red John.
In the season 3 finale when Jane tells Bertram about Hightower, in the very moment that Jane leaves... Bertram picks up the phone... to arrange the fake Red John encounter with Jane. (also in order to cover his back).
He knew about the trap and decided to sell O'glaughling in order to force Cho and Rigsby to run away from the place where the encounter should have took place. So Bertram said the phrase about the "man reached the end of his rope".
Bertram had Jane alone without support. Then left, leaving Jane and the fake RJ alone.
You can notice that Bertram the prevous day was reading the same newspaper that the fake RJ was reading at the meeting. It means that Bertram gave it to the puppet and told him how to behave.
He quotes William Blake in a moment of euphoria. Jane told that RJ would have been euphoric about the capture of Hightower.
Hightower is an accomplice of RJ and the confirmation of this theory is that O'glaughling could have shot her instead of Lisbon. He died anyway so why not fullfilling RJ whish? Why? Because Hightower is an accomplice. And everything was set from the beginning in order to create the perfect trap for Jane.
RJ till now is more capable of Jane. He must be older, more experienced and totally able to play dumb. REMEMBER RJ doesn't want to be caught. Why acting in his full potential in front of PJ? To be caught? Sounds stupid. Bertram shows his weakness (like the one at poker) that he refuses to lose. He plays dumb and there is a conversation between him and Kirkland about the fact that they can't trust anybody. Why? Because Gale Bertram is Red John and Robert Kirkland is his left hand.
He is powefull, full of connections with rich and powerfull people, even in the law forces. He appears when Minelli leaves showing that there was a change in the game between RJ and PJ.
