This is a little complicated, but I will try to simplify it as much as possible.  There was a man who called himself Red John, and he was a serial killer.  He is responsible for the deaths of Patrick Jane's wife and daughter.  Wracked by grief at their deaths, Patrick sought out Red John, found him, and avenged his family by killing him.  This, however, is only the beginning of our story.  You see, Jane is a man who no longer has anything to live for.  His only purpose in life was vengeance on his family's murderer.  Unable to survive now that his revenge has left him empty and unfulfilled, his mind breaks.  He creates a new "Red John" in his mind.  Although Jane is unaware of John presense, it is unclear if John is aware of Jane.  This new personality gives him a purpose and reason to live again.  His dual persona has a second purpose though.  Red John was not just one man, alone.  He had a large network of followers, with members embedded in multiple facets of society, including law enforcement.  By living on in Patrick's mind, this new "Red John" can be used as a tool to smoke out the real Red John's associates and eradicate them.

We only ever see Patrick when he is conducting investigations with the CBI.  What is he doing with the rest of his time?  He seems to be only part of a life, stuck in a moment in time.  Same clothes, same shoes, same car.  He is not fully invested in his own identity any more, because the new "Red John" is very demanding of his time.  Setting up traps to reveal RJ's disciples.  These are most likely people who have never met the real RJ in real life.  Patrick can arrange meetings through other followers, so as to protect his identity.

At the end of last season, it is clearly Simon Baker's voice we hear as "Red John" converses with Patrick.  The timing of the conversation makes it possible that this was a prerecorded message.  Wainwright's silhouette combined with Baker's voice is a tool to throw us off.  You are trying to match the voice to the image, so you don't realize that it is Baker speaking.

The writer's give us other clues to the truth that exist purely as clues, with no basis in the story.  Patrick Jane and Red John are like two halves of a whole.  Yin and Yang.  Patrick is an effeminate man.  Afraid of violence, he only acts confrontational when he has others to back him up.  He drinks tea, and is generally "soft".  Whereas Red John is the violent, masculine, confident half of the pair.  "John" and "Jane" are clear masculine and feminine opposites, and if you search for colors attached to the name "Patrick" (aside from green associated with Saint Patrick's day, which is more an association with Ireland) you will find the cross of Saint Patrick.  It is a red cross on a white background, eerily reminiscent of Red John's signature red smiley face on a white background.

While some are hesitant to accept Patrick Jane as Red John, it should be noted that the only deaths attributable to Red John since the deaths of Jane's family have all been very bad people.  They have either been disciples of Red John, guilty of murder themselves, or other murderers like the San Joaquin Killer (James Panzer).  Therefore, Patrick is not directly responsible for the deaths of any innocents.

The only true way to destroy a man is to destroy his legacy, what he stands for.  For Jane, killing Red John wasn't enough.  He had to cut out the entire cancer, and destroy his legacy.  The only way for Jane to achieve this was to become Red John, himself.

Look the Episode S05 Red Down, look at 6.04 ... What do u see?? Yess a ring, looks that the same that RJ have, in the episode when talks to Rosalind, dont u think? :S

OMG I love this show :D :D..!!

I think it could be Tolman Bunting from the episode, 18-5-4 . He is the one that runs a puzzle store as well as a security firm looking for a code breaker device to read encrypted files. He is caucasian, little less than six feet tall, short hair, slim build, not a deep voice, not quite high pitched but more nasal. Is intelligent, manipulative, knows computer systems, could easily or have someone hack into CBI and/or police computer systems. He enjoyed playing a chess game with Jane, so is competitive, perhaps a sign of enjoying cat and mouse games. What do you think?