The official authority in Venice, the Duke has great respect for Othello as a military man and, unlike the other residents of Venice, does not betray any racial prejudice against Othello and, in fact, is unsurprised that Desdemona fell in love with him. It is the Duke who sends Othello to lead the Venetian mission to defend Cyprus against the Turks.
The timeline below shows where the character Duke of Venice appears in Othello. The colored dots and icons indicate which themes are associated with that appearance.
Act 1, scene 2
Act 1, scene 3
...potions so that she would marry a man she would never otherwise have considered. The Duke promises to help Brabantio prosecute the man who has seduced Desdemona, but when he learns... (full context)
...dramatic tales of travel, battle, and valor. These stories, Othello says, won Desdemona's love. The Duke comments that he thinks his own daughter might be won over by Othello's story. (full context)
Act 4, scene 1
Act 4, scene 2