Elizabeth Tudor is the daughter of Henry VIII and his second wife, Anne Boleyn. She is portrayed by Kate Duggan in Season 2, Claire MacCauley in Season 3 and Laoise Murray in Season 4. She will eventually become Queen Elizabeth I and reign for 44 years.
Elizabeth's personality is not shown to anything of the same degree as her older half-sister Mary, as she is first shown as a newborn in episode 2.03 and as a little girl in most of Seasons 2 and 3; however, it is clear from Anne Boleyn's intelligence, ambition and boldness (traits that would characterize Elizabeth as Queen) that she takes strongly after her mother, and she states to her sister Mary that she does not think boys should be considered more important than girls.
In Season 4 when she is becoming a teenager, her love of reading, dancing and education (encouraged by her father, but likely traits she got from her mother) is shown; she also has something of a mischevous streak, unlike her more religious and graceful elder sister. She is better at concealing her true emotions than Mary, hiding her disdain of Catherine Howard perfectly.
Henry and Anne both loved their daughter dearly (despite hoping she would be a son) but Anne only knew her for a short time; she met her death before Elizabeth was quite three years old. Anne Boleyn would reappear in a hallucination alongside Elizabeth before Henry's death, saying she was proud of Elizabeth's intelligence and boldness; Henry replied that he was proud of her too, but he avoided her sometimes because she reminded him too much of Anne.
Henry declared Elizabeth a bastard (like Mary) after he ended his marriage to Anne and executed her; he cut off the young princess's financial support, claiming that her mother had been a whore and denying that she was his child. However, in episode 3.03 at Christmas, Henry warmly reconciled with the young Elizabeth at the encouragement of his third queen, Jane Seymour and Elizabeth's sister Mary; she was not made heir to the throne, but like Mary she was restored to the royal line. She was also loved by Anne of Cleves and Catherine Parr; Catherine Howard also liked her, but Elizabeth secretly disliked her as much as Mary did.
Elizabeth would later support her sister Mary in her successful bid for the Crown against Lady Jane Grey, but Mary distrusted Elizabeth because of her Protestantism (like her mother) and removed her from the line of succession, locking her in the Tower. However, when it was clear that Mary would have no children with her Spanish husband and she was on her deathbed, she restored Elizabeth to the line of successsion- setting the stage for Elizabeth's impressive 44-year reign, known as the Golden Age.
Elizabeth is shown as a young adult in the fourth season; she has inherited her father's red hair and oval face, but she has the same piercing eyes and pale complexion as her mother. She also has her mother's intelligence, which rather fortunately for her was greater than Henry's; this allowed her to reign with a more objective and less impulsive mind, and she selected her advisors-and dismissed them- more carefully and less often than her father.