Therese's exact age is unknown, but Jeanette mentions their last sunrise as being over two lifetimes ago. Therese was a little girl when she first showed signs of mental illness, namely dissociative identity disorder, which came in the form of an alternative personality called Jeanette.
Therese states that she and Jeanette did get along at one point mainly because she didn't have many friends due to her father never allowing her out thinking that she would get hurt in the outside world, and as a result, Jeanette was the only one who was there for her and they would create their own fantasy world which they would rule over.
Therese's only other known relation from her time alive was her father, who would molest her when drunk. Therese blames Jeanette for his alcoholism, saying that her bad behavior was tormenting him. Therese simply saw this as her being a good and obedient daughter, and she was convinced her father loved her.
Therese's father died later on. The story differs by sister. Therese says their father killed himself because Jeanette was a bad daughter and tormented their father with her promiscuity. Jeanette says that their father came home drunk one evening and mistook Jeanette for Therese and began molesting her instead. Therese caught them together and in a jealous rage she shot him with one of their father's hunting rifles, "splattering his brains all over the silly clown wallpaper".
The police found out about his death and noticed one of her personalities had killed their father. It is heavily implied Therese was placed in a mental institution, where they briefly suppressed Jeanette from Thereses's mind, and she must have remained at the institute until young adulthood. Jeanette mentions an escape, saying the first thing Therese did was find Jeanette. It is likely she is talking about her embrace by an unknown Malkavian, which may have brought about Jeanette's return as Malkavian blood is inherently insane.
Therese rose to power in Los Angeles as the Baron of Santa Monica and as a successful businesswoman. Her base of operations and her primary business source was The Asylum, a nightclub in her barony. She ran through finances and business things, while Jeanette lured in patrons for the club.
When the Camarilla became a presence in Santa Monica once again under Prince Sebastian LaCroix, Therese sought to ally herself with him and the Camarilla. Jeanette favored the Anarchs and was in direct contact with Smiling Jack. It can also be assumed that Therese or Jeanette is responsible for Lily being held prisoner in the blood bank, because the Thin Bloods were forbidden to hunt in the Santa Monica area and Lily was caught stealing from the blood bank and was captured by Vandal, Therese's ghoul.
Therese had invested in many new business ventures, one of which Bertram Tung and Therese's sister Jeanette ruined for her, causing a feud between her and Tung. Tung was so scared of Jeanette that he went into hiding. Her most promising was The Ocean House Hotel. The Ocean House opened in the early 20th Century and was a popular and modern destination for vacationers. However, an insane guest and his family stayed and the man decapitated his wife and children, and one of his children's heads was found in the dryer in the hotel laundry room. This scandal hurt business, and Ocean House was abandoned.
Therese decided to invest in the property and set a team of designers and construction workers onto it, however, a ghostly presence haunted the building and scared off all the workers. Therese had very few options left except to follow folklore and superstition. She assigned the protagonist, who had been sent to her by the Prince's ghoul, Mercurio, to retrieve an artifact from the site in order to exorcise the spirit from the site.
After retrieving it, the protagonist has two options: give it to Therese and allow her to improve her business; or give it to Jeanette, who will throw it into the Pacific. Either way, Jeanette will manipulate the player into ruining another of Therese's businesses, Gallery Noir, an art gallery for which Therese was using to host a charity event for many influential Santa Monicans. Jeanette persuaded them to slash the painting, which depict Caine, the first vampire, and also to steal money from the charity box. However, Therese had placed a Thaumaturgical enchantment on the paintings, so when they were slashed they summoned the Blood Guardian, a humanoid creature composed of blood with black claws. Jeanette reveals to Therese her trickery, leading Therese to be furious when you return to her, but she'll calm down once you give her the Ocean House Necklace.
Therese herself tries to finish the protagonist off, she lies to you and says she seeks to reconcile with Jeanette who's been avoiding Therese after Therese threatened to set Jeanette's prized satin sheets on fire. Therese wanted to meet up with her at the Surfside Diner across the street from the Asylum, but she says she is busy with the club and sends the protagonist instead. However it is a setup and one of the sisters, depending on which one the pendant was given to, has sent a gang of thugs to kill the protagonist. No matter who is on the other end of the phone, a hint is given that Jeanette is in danger.
When you arrive at the Asylum, it initially appears that Therese is holding a gun to their bathroom door, presumably with Jeanette hiding inside, but when she turns around, one side of her face has its hair tied back and without make up, like Therese, with the other having one side of its hair in a pigtail and Gothic make up like Jeanette. Therese intends to murder Jeanette.
There are three possible fates for Therese. You can kill off Therese's personality and have Jeanette become the dominant personality, kill off Jeanette and have Therese regain full control of her body, or make the sisters realize they do care for each other and encourage them to cooperate together. Either way, you are led to Bertram Tung, the Nosferatu who has been conspiring with Jeanette against Therese. If you side with Therese, Santa Monica becomes aligned with the Camarilla, and if you side with Jeanette, it becomes aligned with the Anarchs. There is a possibility of being able to have sex with Jeanette if the protagonist used Seduction on her.
As a person, Therese is very intelligent, arrogant, ruthless and cunning, with a superb mind for business, however, she is not without morals, she genuinely cares for Jeanette and believes she is responsible for Jeanette's survival as a vampire. Therese is also something of a prude, she is extremely pious and chaste, and thinks vampires superior to humans, expressing her disgust at the thought of Jeanette having sex with mortals. She fancies herself better than the average Malkavian, as she is not so open about her clan heritage as her sister is and like most Ventrue or Toreador vampires, looks down on the Nosferatu, especially Bertram Tung.
Jeanette is highly sexually promiscuous having numerous lovers, including various mortals and potentially the protagonist. Jeanette is very childish in most things she does, she is very needy and uses a mix of her childish nature and potent sexuality to get what she wants, also she often makes petty quips about Therese, calling herself the "Prettier Face" and mocking Therese's piousness and snobbery calling her "Queen Victoria" and "The Virgin Queen of the Night".
One thing they both have in common is that they both believe themselves to be the "good" sister, when it comes to certain areas, particularly their father. While Jeanette sees Therese's incestuous molestation by their father as Therese being just as sexually depraved as she is, whereas Therese saw it as being an obedient daughter. Jeanette despite being rather friendly, is perfectly capable of malicious acts such as when she asks the protagonist to rob the charity box at Therese's art gallery. Whilst Therese who is as cold as ice and as tough as nails, softens to her sister when remembering happier times when they were little and all they had was each other.
Besides Therese's split personality, Therese and Jeanette seem to have their own mental illnesses. Jeanette is a hypersexual nymphomaniac, which explains why she still fornicates, whereas Therese seems to suffer from obsessive compulsive disorder as she shuns physical contact, indicated by Jeanette who says Therese won't drink blood out of anything other than a wine glass and her disdain for sex, as well declaring many things as unclean, including Nosferatu. Jeanette doesn't have any problems with the Nosferatu, having relations with Bertram Tung and the protagonist, if (s)he is one of the Sewer Rats.
- In the Vampire: The Masquerade sourcebook - Los Angeles by Night, the vampire leader of Santa Monica was Louis Fortier, Baron of West Los Angeles, a 9th Generation Ventrue who ruled over Santa Monica, Beverly Hills, Pacific Palisades, Venice and Marina Del Rey. It could be assumed that Therese is his successor and that she has wrestled control from him.
- Jeanette posed nude for a photo; the photo ended up in the possession of Nosferatu primogen, Gary Golden. It is obtainable through an unofficial quest done by email with Gary, he will trade this photo for a copy of one of his old films, Tap Hotel.
- Harley Quinn's design in the games Batman: Arkham Asylum and Batman: Arkham City, took influence from Jeanette Voerman, especially her blonde pigtails.
- She is nicknamed 'Daughter of Janus' (Janus being the Roman two-faced God) by the Malkavian Protagonist. This is due to their gilf of insight and a hint to Therese's split personality.