Who is Mrs. Cheveley from the play, An Ideal Husband?

Mrs. Cheveley, the villain of Wilde's play, enters the society of the Chilterns and Lord Goring determined either to get her own way or to destroy those who will not help her achieve her ends. She comes to London from Vienna, where she has been living for some time, to blackmail Sir Robert Chiltern. She knows Chiltern's terrible, scandalous secret and has concrete evidence of his transgression (a letter he wrote). She informs Chiltern that she will expose his sinful past unless he praises a South American canal scheme instead of condemning it for the stock market swindle it is as he plans to do in a parliamentary speech.