Ignoramus is the title of a play by George Ruggle that was first produced in 1615. The play is a farce set at Cambridge University and has as its main character a magistrate who believes himself to be shrewd when in fact he is foolish and ignorant. This character's name is Ignoramus, which in Latin means "we do not know." In the course of the play, Ignoramus is subjected to a series of humiliations. He is denied the woman he loves, saddled with a shrew, subjected to a sound drubbing, judged to be possessed by evil spirits, subjected to exorcism, and packed off to a monastery.
In Ruggle's time, the word ignoramus was used in legal proceedings. Grand juries would write ignoramus on bills of indictment when the presented evidence was insufficient to justify prosecution. In these cases ignoramus indicated "we take no notice of, we do not recognize this indictment." It seems likely that it was from this legal use that Ruggle took his character's name, especially when we consider that Ignoramus of Ruggle's play was based on an actual Cambridge magistrate who was embroiled in an ongoing feud between the town of Cambridge and the University.
Ruggle's play was an instant success, and it was not long before ignoramus came to be used allusively as a contemptuous term for any woefully ignorant person.