who is the jackal in chapter 5

That would be Carton. Mr. Stryver is prone to alcoholism, and he is a drinking companion of Mr. Carton's--they had been fellow students in Paris. Mr. Stryver, despite all of his capacity to push himself ahead, became a much more successful lawyer when Mr. Carton began working on and helping summarize his documents for him. Thus Carton became Stryver's jackal. When Stryver talks about how pretty Miss Manette is, Carton denies it, claiming she is nothing but a blond "doll."Carton leaves Stryver's house and returns to his own, crying himself to sleep. He is haunted by the honorable glories that once were available to him but are now out of his reach.

tale of the two cities