Who was Bianca? How did Iago use her against Othello? (thank you so much:)

Bianca

A courtesan who Cassio visits frequently; Cassio asks her to make a copy of Desdemona's handkerchief, and the fact that the handkerchief is found in her place further incriminates Cassio. She is the only female in the play whom Cassio shows less than full respect to, likely because she is a prostitute.