Why did Othello Kill Desdemona and himself? OR, Who was responsible for the death of Desdemona and Othello?

Answer: Othello Promoted Cassio to the post of Lieutenant and it made Iago furious and jealousy because Iago was senior to Cassio and more fit for the post than Cassio. Anyhow, he wanted to take revenge against both Othello and Cassio. He could not tolerate that biased decision of Othello. Anger consumed Iago. He immediately planned and scandalized Othello’s wife Desdemona before Othello and made Othello believe that she had an extramarital affair with Cassio. Iago also proved her to be an unfaithful lady. Othello became very angry and out of suspicion and anger, he killed his wife Desdemona by strangulation. 

After the murder, when he realized that he had made a blunder and found his wife innocent, he killed himself by stabbing.