Diego the Dreadful was a Spanish pirate who appeared in The Secret of the Unicorn in The Adventures of Tintin series. Diego was the faithful first mate of the infamous piratecaptain Red Rackham. He is first seen as he challenged Sir Francis Haddock in a duel after the later kills or wounds several of his companions during the attack of the Unicorn. As Archibald Haddock was role-playing Sir Francis, he was now revealed as he was stabbed on the belly, when Archibald stabbed his pillow cushion and Red Rackham explaining to the captured Sir Francis that Sir Francis killed Diego of screen.
Diego never appeared in the animated series. Instead its Red Rackham himself who challenge Sir Francis in the duel before he faint thanks to a powerful hit in his head.