Thomas is a noble of the vamperic white court, only surviving son of the white king. He is also Harry Dresden's older half-brother (they share the same mother: Margret LeFay).
He was disowned by his family (see Blood Rights) after a internal family fight. He lived with Harry for a little wile after this before moving into an apartment of his own in Chicago's 'Gold Coast' area. He got a job as a beautician to support himself after being cut off from family funds.
After being abducted and tortured by a shape-shifter in the book Turn Coat, he returned to his family admitting his mistake of ever trying to defy the creature he is inside.
Subsequently, because of the looks that come with the powers of his family, Thomas attracts a fairly large crowed of both women and men, and thanks to the Raith 'Come hither' powers of attraction, when he's 'hungry', humans don't stand a chance.