Thomas Raith is a vampire of the White Court and only surviving son of Lord Raith. We first meet him at Bianca's ball in Grave Peril. His personality is perhaps best described in Blood Rites: "Thomas was an annoying wiseass who tended to make everyone he met want to kill him, and when I have that much in common with someone, I can't help but like him a little."
White Court vampires do not drink blood. Rather, they fed on emotions, drawing the life energy from their prey through them. For the Raiths, this is usually during sex. However, love is poisonous to them, and they are incapable of feeding off anyone recently touched by love.
Thomas is about six feet tall, pale as a statue, and has the physique of "the forgotten Greek god of body cologne." He has black, shoulder-length, naturally curling hair and grey eyes that go completely white when tapping his demon's energy.
Warning: The following contains spoilers for later books. Read at your own risk.
Developments throughout the series
Grave Peril - We meet Thomas and his lover Justine at Bianca's party. Thomas gives Harry a primer in vampire court politics, and Justine coerces Harry into making sure she and Thomas get out alive. When Justine and Susan are captured, Thomas manages to steal back Amoracchius from Bianca and offers it to Harry and Michael in exchange for their help rescuing Justine.
Death Masks - Thomas is named Duke Ortega's second in his duel with Harry. He secretly conspires with Susan and the Fellowship of Saint Giles to ensure Ortega doesn't kill Harry, and he generally does his best to preserve his appearance as a politically harmless, "drunken, chemical-besotted playboy who does nothing but cavort, sleep, and feed."
Blood Rites - Thomas asks for Harry's help investigating a series of suspicious deaths surrounding a friend. Along the way, we meet several members of Thomas' family, including his older sister Lara, his father Lord Raith, and his teenaged sister Inari, who has not yet come into her White Court powers. When Thomas asks Lara's help in overthrowing their father, she shoots him, nearly killing him. Justine sacrifices her life to save him and only barely survives. The next morning, a fully-healed yet despairing Thomas reveals to Harry that he is also son of Margaret LeFay, making them half-brothers. Lord Raith moves to kill Harry and Thomas in order to end Margaret's curse on him, but they manage to thwart his plans. Lara takes over as leader of the White Court with the weakened Lord Raith as her puppet. However, in order to keep up appearances, she is forced to cut Thomas off from House Raith and by extension Justine, whose love for him now makes it impossible for him to touch her without suffering severe burns.
Dead Beat - Thomas struggles with trying to "fit in" as a human. He is fired from every job he attempts when his assorted coworkers (male and female alike) attempt to molest him on the clock.
Proven Guilty - Thomas, behaving in an unusually mysterious and cagey manner, moves out. He has a new job that he refuses to tell Harry about and he reveals that he has been feeding again.