Atticus, who rarely has a bad word to say about anyone, refers to the Ewell family as
... the disgrace of Maycomb for three generations.
Bob is certainly the most evil character in the novel: Crude, rude and completely socially unacceptable, he beats his daughter (and possibly even has sexual relations with her); fails to provide for his children or see that they go to school; drinks up his paycheck; falsely accuses a man of a capital crime which leads to Tom's death; stalks Tom's wife, Helen, and croons "foul words" to her; threatens to kill Atticus; and, eventually, tries to kill Atticus's children.
Robert E. Lee Ewell is named after the South's greatest hero, but he certainly does not honor the name: "We also saw no resemblance to his namesake." Scout describes Bob as a "little bantam cock of a man" who "strutted" to the witness stand at the trial. His
... face was as red as his neck.
He was a "little man" who had apparently taken a rare bath for the occasion, since it was the only thing
... that made him any better than his nearest neighbors... if scrubbed with lye soap in very hot water, his skin was white.
... wispy new-washed hair... his nose was thin, pointed and shiny; he had no chin to speak of...
He chews tobacco, as Atticus finds out the hard way; and he often smells of alcohol, as Scout notes when they are attacked on Halloween night. Racist, angry and hateful to nearly everyone he encounters, Bob is the epitome of "trash."
descibe him as a liar and a racist and a person who could kidnap because he wanted to do that to Scout and Jem after the case and the halloween costume party, and a liar because he forced Mayella to blame Tom Robinson when he wasn't guilty of the rape or sexual assault that they were talking about. Also a racist because i remember that he told Atticus that a why would he believe a Negro but not a person of his own color and also a person like him. So that is how Bob Ewel can be desribed.