Rosalind Harker is the mastemind behind the Red John Organisation and she comes from the past of Jane's life.
Red John is Jane's opposite even though more than a single person, Red John is an Organisation. Jane himself is the cause of some of their crimes. Both good and evil, angel and demon, come from Jane's past, like Jane himself, first he was a fraud and conman, then a person who helps other people.
Rosalind Harker herself is connected somehow to Jane's past and Roy Tagliaferro and the others are simply the executors of her plans.