The Mentalist creator Bruno Heller has been quoted saying he is a big fan of anagrams and other such word puzzles.
Red John is an anagram for Hjorden
Hjorden or Hjord in Swedish/Danish: herd; a number of beasts gathered.
This could be evidence that Red John is indeed an alias that a number of people are using (possibly explaining the suspicious meeting between Bertram, McAlliser, and Reed).
The biggest "clue" about Red John (apart from the basic physical parameters we already know: Caucasian, male, mid 30s early 40s, and around 6' tall) is the poem "The Tiger" by William Blake. One of the themes expressed in this poem is Blake's "bewilderment that the God who created the gentle lamb also created the terrifying tiger, he includes Satan as a possible creator" (Michael J. Cummings 2003. Study Guides. Web.). In S6E1, as Lisbon is walking through the house we see the word "DIE" along with a pentagram and "666" (the number of the beast) scrawled on the walls in what appears to be blood.
This could reveal that Red John is truly an embodiment of the evil of men, with each of it's primary members representing a different aspect of evil (7 suspects, 7 deadly sins?).
Another clue...episode 8 of season 6, in which we're supposed to learn of the identity of RJ, is entitled "The Great Red Dragon". This is the name for a series of paintings done by Blake. The subject matter of these paintings is Satan from the book of revelations. In these paintings he is depicted with 7 heads and 7 crowns (7 suspects guys!!).
Now, lets look at the 7 Red John suspects and how they relate to William Blake and his poetry (as this poem/Blake has been a motif throughout the series). I realize some of these may be a stretch, so any comments/help on more concrete relationships to Blake would be awesome!
1. Brett Partridge: A Brace of Partidge is a painting by Blake
2. Bret Stiles: William Rosseti Blake....The name Bret Stiles comes from rearranging some of the letters
3. Gale Bertram: He quotes the Blake poem "Cradle Song", a poem about losing innocence
4. Reede Smith: Reeds of Innocence (poem by Blake)
5. Thomas McAllister: Blake had a friendship with Thomas Paine
6. Ray Haffner: No idea....
7. Bob/Robert Kirkland: No idea....
As you can see there are still areas of this theory that need fleshing out.
One more piece of evidence..."He is mar" could mean "He is many".
