How does Alonso, the king of Naples, die in Shakespeare's The Tempest?
In The Tempest, Ariel, the spirit, tells Ferdinand, King Alonso's son, that his father has drowned. In Act 1, Scene 2, Ariel sings,
"Full fathom five thy father lies. Of his bones are coral made. Those are pearls that were his eyes. Nothing of him that doth fade but doth suffer a sea change into something rich and strange."
Ferdinand spends most of the play, then, thinking his father has drowned in the shipwreck that resulted from the tempest. Previously in this scene, however, Ariel has assured Prospero that all the men aboard the ship are safe, but that he has "in troops ... dispersed them 'bout the isle."
In Alonso's troop are Sebastian, the King's brother, and Antonio, Prospero's brother. Alonso comes close to death by assassination by Sebastian and Antonio as he falls asleep under Ariel's spell. Ariel wakes Alonso up just as the two diabolical plotters have drawn their swords on their king.
So although Alonso does not die in the play, Ferdinand thinks he has drowned in the shipwreck, and he is the victim of an attempted murder by Antonio and Sebastian.