Mr. Thorpe is mentioned in Northanger Abbey, but is long dead before the course of the novel, so he does not make an appearance. He was married to Mrs. Thorpe and had at least four children with her: John, Isabella, Maria, and Anne. Mr. Thorpe had been a lawyer while he was alive.
The family was not incredibly well-off, although they were comfortable. This made it so Mrs. Thorpe was very interested in finding wealthy spouses for her children, namely her two elder children, John and Isabella. They rather shamelessly targeted the Morland family because they believed them to be incredibly wealthy. This was a mistake on their part, however, as the Morlands were not charlatans.
Mr. Thorpe's profession also closed a lot of doors to the Thorpe children, as gentlemen and gentlewomen would be less likely to marry John and Isabella. Therefore, they had to go after those who wouldn't make such an issue out of their lack of connections and breeding, like the Morlands. Isabella's quest to snag Frederick Tilney was a failure from its conception, as there would be no way General Tilney would be pleased with such a match unless they eloped.