Final answer:
The Duke sends for Othello to command the defense of Cyprus against the Ottoman Turks threat due to his military expertise and leadership qualities.
Step-by-step explanation:
The question pertains to why the Duke summons Othello in Shakespeare's play 'Othello.' The answer lies in the geopolitical situation facing the island of Cyprus, which is under threat of invasion by the Ottoman Turks. The Duke entrusts Othello with the defense of Cyprus due to his renowned military prowess and leadership.
Othello's favorable reputation as a valiant soldier makes him the ideal candidate to lead the Venetian forces against the impending danger.