A Sweden from a rich and powerful family. His dad was Count Fredrik Axel von Fersen, who was the field marshal, councilor of the empire, founding member of the Academy, and leader and elder of statesman of the party of the old nobility. The family had originally came from Scotland. (So, it was not a surprise in Episode 18—"Suddenly, Like Icarus" that he mentioned his dad arranged a marriage for him with a British lady Ms. Diesel. However the lady’s name was not found in history).
He was the eldest son of Count Fredrik Axel von Fersen. Not only rich and powerful, but Fersen was described as well-educated, handsome man with good body.
He went abroad in 1770, on a tour lasting four years in the course which he attended in Brunswick Military Academy and the University of Turin. He paid a brief visit to Paris during that four years in January 1774. It was that time when Fersen met Marie Antoinette in episode 7—"Who Wrote the Love Letter". However, he met Marie Antoinette in other Versailles balls before the Paris masquerade.
Like episode 20—"Fersen, a Farwell Rondeau", there were lots of gossips about the relationship between Fersen and Marie Antoinette. He went to America with the French troops to fight with the colonists during the American Independence war, as the escape from the court gossip.
His dad arranged marriage for him with an English lady Miss Leijel. At that time he thought the marriage would bring advantages to him. He kept writing letters to Miss Leijel, but did not get a reply. Later on, he found out that she was married. Actually he felt relief because of his true love with Marie Antoinette. Another lady that almost became his wife was the daughter of Monsieur Necker, the Finance minister of France.
In the history, Fersen was described as the playboy. When he was in Italy, he had relationship with Lord Cowper’s stepsister, Lady Elisabeth Foster, etc. RoV, of course, did not mention those love affairs to show his true and deep love with Marie Antoinette.
After the American Independence War, Fersen came back to Versailles and became the colonel of the Royal Sudois, like episode 25—"A Minuet of Unrequited Love". The love between Fersen and Marie Antoinette became more matured. He wrote letters to Marie Antoinette by calling her "Josephine". In the letters, they discussed petty things like naming the Sweden hunting dog.
Fersen wrote letters to his beloved sister Sophie to describe his deep feelings. He told her that he fell in love with a person that he could never be together with. Therefore he decided not to marry for the rest of his life, and Sophie should take care of the house.
Fersen arranged the flight for the royal family in 1791, which was unsuccessful. After that, he kept on communicate with Marie Antoinette with ciphered letters, hidden in chocolate box, hats, etc. and tried to arrange another escape. But Louis XVI refused.
After Marie Antoinette’s death, he went back to Sweden. There were rumors that Fersen had poisoned the Crown Prince in Sweden. It was known in advance that riots were being organized for the day of the Prince’s funeral. People notified the King of the possible attack and advice that Fersen should not show up. The King answered, "it would be no bad thing if this proud gentleman were to be taught a lesson".
The mob spat Fersen’s coach, then broke its windows with paving stones and at last dragged Fersen out into the road. A sailor killed him by jumping on his chest as he lay in the gutter.