Mercia Cavendish
Mercia Cavendish
Biographical Information
Full name

Mercia Morgana Cavendish


March 17
Chatsworth House, Derbyshire Dales, England





Blood status


Physical Description


Hair color

Almond Truffle

Eye color

Dark Brown


168 cm


Myror Cavendish (father)
† Eliza Cavendish (mother)


Mordred Myror Cavendish (younger twinbrother)
Arthur James (maternal illegitimate younger brother)

Significant Other

Peregrine Cavendish (paternal first cousin)
Edward Spencer (fiancée)

Magical characteristics

13¾", Yew, Thestral tail hair core






Slytherin student


Lady Cavendish
Lady of Devonshire
Marchioness of Hartington
Countess of Burlington
My lady
Her Ladyship
Your Ladyship


Chatsworth House, Derbyshire Dales, England
Bolton Abbey, Wharfedale, North Yorkshire, England
Lismore Castle, Lismore, County Waterford, Ireland

Hogwarts School of Witchcraft and Wizardry




House of Cavendish

Hogwarts School of Witchcraft and Wizardry
Slytherin ● Slytherin Quidditch team

Lady Mercia Morgana Cavendish of Devonshire is the only daughter and eldest child of the Duke and Duchess of Devonshire.

Mercia is willful, ambitious and has a certain low cunning. She is, in her opinion, politically astute and thinks of herself as her father's daughter, and feels slighted when people do not jump to her erratic commands. She resents the customs and conventions put on her because of her gender, but never realizes that people do not come to her or respect her commands because she is an ineffectual leader.

By tricking her brother, Mordred, and first cousin, Peregrine, into the religious life of celibacy they officially declined their birthrights as Duke of Devonshire making Mercia the only heir to the Dukedom of Devonshire.

The more power Mercia obtains, the more she proves herself to be incompetent at handling it; although she has spent most of her life scheming to gain power, she seems to have little idea of what to do with it once she has it.

She is a Slytherin student at Hogwarts School of Witchcraft and Wizardry at her seventh year, as well as a part of the Slytherin Quidditch team.

By her father engaged to Edward Spencer, Marquess of Blandford from the age of 5.


Early life (age 0-11)

Mercia is technically her parents' oldest child, although her twin Mordred was born mere moments later, clutching her heel. The twins were eight years old when their illegitimate brother Arthur was born, killing their mother and causing their father to become cold and bitter.

Her father, Myror Cavendish, is the head of House Cavendish, one of the richest and most influential aristocratic families in England since the 16th century, and has been rivalled in political influence perhaps only by the Marquesses of Salisbury and the Earls of Derby. They are descended from Sir John Cavendish of Cavendish in the county of Suffolk (c. 1346–1381).

Mercia is the elder twin of Mordred Cavendish and the elder sister of her mother’s illegitimate child, Arthur James. She was raised in privilege in the family seat of Chatsworth House. She is noted for her great beauty.

Mercia's mother died when she was four years old, after giving birth to her illegitimate younger brother Arthur James. Like her father, Mercia has always blamed Arthur for her mother's death and deeply resents that her mother died so that Arthur would be brought into the world. Mercia's father Myror was constantly away from home during her childhood and teenaged years, serving as British government minister in London, with only infrequent visits back to his seat at Chatsworth House. Coupled with the death of her mother, this meant that Mercia and her twinbrother, Mordred, were primarily raised by servants attached to House Cavendish.

Securing her title

Sometime during her childhood Mercia manipulated Mordred and persuaded him to join the Church, which would require him to live in celibacy meaning never being able to produce an heir and therefore declaring his birthrigh as a man to become the Duke of Devonshire. She expected that Duke Myror would be strictly opposed to the idea, but that he would not dare to openly object to it in order not to offend the Queen.

She made the same number with the second and final male heir to the title: Her first cousin Peregrine.

This way she is now the rightful heir to the Dukedom of Devonshire. The first female to hold the title.

Hogwarts years (age 11-present)

When entering Hogwarts School of Witchcraft and Wizardry Marcia was sorted into Slytherin House.

Her brother Mordred refused to enter as the Church had told him magic is the Devil's work. He was therefore sent to a Monastery in order to start his education as a monk.

Mercia had no truble being apart from her twin-brother. She knew he would have been sorted into Hufflepuff – a disgrace to her family and noble name!

Physical description

Mercia is a strikingly beautiful woman with classic Cavendish looks: Almond truffle hair, deep dark brown eyes, fair skin, and a slender, graceful figure.

Personality and traits

Mercia is willful, cold, ambitious, and cunning in the sense that she is utterly willing to betray anyone who trusts her, or do anything to protect her own. However, she is also arrogant and self-centered to a fault. While she certainly believes herself to be a master strategist, she is extremely impatient, short-sighted, and prone to displays of poor judgment, resulting in her being unskilled at manipulating enemies who openly distrust her. Mercia's own father Myror stated to her that he distrusts her because she isn't nearly as intelligent as she believes herself to be. This makes for a dangerous combination, as not only is Mercia unintelligent, but she does not even realize her own limitations.

A mistake outsiders often make when dealing with Mercia is assuming that she has the emotional maturity and wisdom of a queen, or at least an adult, when her real personality is closer to a petulant child inhabiting an adult's body. With her mother dead at a young age and her father away at court (and a cold disciplinarian anyway), Mercia was functionally raised by servants. In public, Mercia often tries to exude a sense of calm and regal control over her surroundings. When things do not go her own way, however, Mercia's usual response is to become childishly flippant. She also has a tendency to irrationally blame other people for problems she actually started herself though her ego won't let her admit otherwise.

Mercia's behavior is very mercurial, capable of switching between seemingly true affection for someone to extreme loathing over trifles. She is very petty about even small slights, but real and imagined. As Arthur noted, Mercia often uses her honest feelings to dishonestly manipulate other people. For example, her fear for the safety of her loved once is actually genuine, but she will shamelessly use this to play on the sympathy of other people, to sway them into supporting her.

Mercia despises the restraints placed on her because she is a woman and is jealous of the freedoms that men have in her society. Several of the noble Houses in the United Kingdoms have more liberal attitudes when it comes to involving female members of their family in politics. Unfortunately, Mercia's father Myror is a staunch conservative, and never envisioned Mercia playing an active role in politics. Instead, her duty was to cement a marriage alliance and raise noble children, nothing more. It is also possible that instead of her gender being the object, Myror believes she is simply too impatient and rash. Either way, the practical result is that, right or wrong, Myror didn't raise Mercia to be skilled in ruling or in political intrigue. While confronted with these shortfalls, Mercia often blames her father or society in general for not giving her the years of training needed to rule, but complaining about it doesn't change the fact that she simply doesn't possess these skills. Mercia hates being a woman in the English society, and scorns other women in general for what she perceives as their weakness: Mercia isn't so much angry at men for mistreating women, as angry that she isn't a man. When she was drunk during a party once, she even openly said she wished she was born a man.



Edward Spencer

Although once optimistic about her noble engagment to Edward Spencer, she quickly grew to despise him as a Hufflepuff fool who remained too infatuated with the memory of Lana Stuart to give her a second glance.



Mercia's feelings toward her father are complex; she resents him for marrying her off to Edward Spencer and for never granting her as much power and respect as she craved, but also admires and seeks to emulate his brutal effectiveness as a politician.

Arthur James

She has loathed her illegitimate younger brother Arthur ever since his birth killed their mother.

Mordred and Peregrine Cavendish

The only people she truly loves are her twin brother Mordred Cavendish and her first cousin Peregrine Cavendish. However, she seems to love Mordred and Peregrine more as extensions of herself than anything else, and can turn on them suddenly: while she protects her family fiercely from any others who would harm them, she provides them with little in the way of sound guidance or consistent discipline, and can react abusively when they defy or disappoint her.


  • Based upon Cersei Lannister from Game of Thrones.
  • Model is Nina Dobrev.

See also

v - e - d
Hogwarts Seal
Gryffindor Seal


Hufflepuff Seal


Ravenclaw Seal


Slytherin Seal

Ella Avery | Mercia Cavendish

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