Lady Jane Boleyn (nee Parker), Viscountess Rochford is the ill-fated wife (and later widow) of George Boleyn, Lord of Rochford, in The Tudors. She is played by Irish actress Joanne King in a recurring role in Seasons 2 through 4. She is a servant to five of King Henry's wives (Catherine of Aragon, Anne Boleyn, Jane Seymour, Anne of Cleves and Katherine Howard) before she is finally beheaded in episode 4.05, for her involvement in Katherine Howard's adultery against the King.
Jane in introduced as the betrothed of George Boleyn, though she is clearly reluctant to be married and frightened at the thought of her wedding. Nevertheless, Jane's father forces her down the aisle (2.06).
Jane is at first uncertain of what to make of George (unaware of his previous libertine lifestyle) and, although he is relatively friendly towards her at the reception, her opinion changes sharply when George holds her down and rapes her on their wedding night before he collapses on his bed, drunk.
In spite of her fear and anger towards him, Jane initially tries to make the relationship work. However, she is quick to notice George's frequent absence due to his many affairs, and observes him talking discreetly with the (closeted) court musician Mark Smeaton. She confronts George about his various infidelities and is horrified when he doesn't bother to deny his affairs both with women and with Smeaton; although she is a supporter of the Reformation, Jane firmly believes homosexuality is still a cardinal sin (2.08).
Jane attempts to plead for help from George's sister, Queen Anne Boleyn (whose relationship with King Henry is currently strained), but Anne, while not acting cruelly, nonetheless gives her little sympathy and refuses to acknowledge George's unpleasant character, earning her Jane's anger.
When Henry's dissatisfaction for Queen Anne finally comes to a head, Jane is one of the handmaidens Thomas Cromwell interviews about her supposed acts of incest and adultery. Although she knows the accusations of incest are ridiculous, Jane - already resentful towards the Queen for not helping her - unhesitatingly says the Queen is guilty of an incestuous relationship with George. Cromwell looks at her in astonishment before he sees the knowing smile on her face; he returns it with one of his own (2.09).
Though Jane exacts her revenge on George and Anne, her fortunes ultimately plummet after her husband and sister-in-law are beheaded. She is shunned by many of the court either for being an associate of the scandalous Boleyn family, or for supporting the accusations that some (correctly) assumed were false. Jane is left with no significant property, as Hever Castle and most of George's wealth were forfeited to the Crown for his "treason".
Season Three 
Season 3 opens up new opportunities for Jane when she is taken as a Lady-in waiting by Anne's successor, Queen Jane Seymour. The new Queen kindly acknowledges that Jane did not bear responsibility for George's actions (though not specifying whether the 'actions' in question were of incest - which were false- or his cruelty to his wife) and asks her to be her principal lady-in-waiting. Despite the Queen's devout Catholicism, Jane happily accepts.
Jane acts as the new Queen's main confidant and friend, informing her of Henry's infidelities with Lady Missledon. The Queen graciously chooses to ignore his infidelity and instead focus on small favors, such as providing money for Henry's disfavored young daughter Elizabeth (whom Jane bears no grudge against, despite her anger towards Elizabeth's mother)(3.04).
Unfortunately, the Queen dies shortly after giving birth to the long desired male heir, leaving both King Henry and Jane heartbroken. Jane later serves as handmaiden for Queen Anne of Cleves, and comforts her in the Season finale when Anne's marriage to Henry is abruptly annulled.
Season Four 
Jane is made lady-in-waiting to the King's fifth Queen, Katherine Howard. Though she carefully hides it, Jane takes an instant dislike to Katherine Howard for her immaturity, flirtatious nature and stupidity; she is also angry with her for displacing Anne of Cleves, whom she liked. Jane learns details of Katherine's scandalous past from another lady-in-waiting and friend of Katherine's, Joan Bulmer and plans to use it against the young Queen.
Jane begins a sexual relationship with the King's arrogant groom, Thomas Culpepper, and suggests to him that she can arrange for him to have sex with the Queen. She is aware that Thomas desires Katherine, and hopes to use this to somehow disgrace or corrupt Katherine further. Unfortunately, when this affair is discovered, Jane is caught up in the storm when Culpepper names her for bringing him and Katherine together, revealing that she is culpable for having arranged all their liaisons (4.05). Jane is arrested and questioned by Thomas Seymour, and suffers a nervous breakdown to the point that she is declared legally insane and placed in the Tower of London.
Henry's vengeance is wide-ranging; however, and he pushes a bill through Parliament making it legal to behead insane people. The broken-down Jane is quickly sentenced to death and brought to the same scaffold as Katherine Howard at Tyburn. Jane hysterically puts herself on the slab first after a few muttered words.
Jane is quickly beheaded, with Katherine suffering the same fate moments later.
Backstory of the real Jane Boleyn
Jane Parker was born c. 1505 at Great Hallingbury Manor in Essex to Henry Parker, 10th Baron Morley and Alice St John. She was related to the Beaufort family, and she was a cousin of King Henry VIII. At some point when she in her early teens, she was sent to court to serve Katherine of Aragon as a maid of honour. She was one of the English noblewomen present at the Field of the Cloth of Gold in 1520, she also took part in the Château Vert pageant alongside Anne Boleyn and Mary Boleyn. Jane played the role of Constancy, Anne played Perseverance and Mary played Kindness.
In 1524, she and George Boleyn got married, it has long been said that the marriage was unhappy, however historian Julia Fox wrote in her book Jane Boleyn: The Infamous Lady Rochford that there is no evidence to suggest that the marriage was unhappy nor that her relationship with Anne was a bad one, because Anne shared with Jane details about King Henry VIII's sexual problems, which is not something that enemies would do.
In 1536, George was executed under the charge of incest and treason, Jane is said to have given false evidence that George committed incest with Anne, however all records suggest it was another of Anne's maids, the Countess of Worcester who gave the incest evidence, Jane even sent a comforting letter to George, saying that she would try to get an audience with the King's council. Jane was questioned by Cromwell, but according to Historian Eric Ives, Jane's confession did not contain incest or adultery, but simply something that Anne said about the King's inability to please her sexually.
She returned to court to serve Jane Seymour and Henry's next two wives. In late 1541, Katherine Howard's past indiscretions were uncovered and Katherine was taken to Syon Abbey and Jane to the Tower. She suffered a nervous breakdown and was declared insane, she was condemned by an Act of Attainder and was executed on 13 February 1542 with Katherine Howard at Tower Green.