A Connecticut Yankee in King Arthur’s Court (1949)

A bump on the head sends Hank Martin, 1905 auto mechanic, to Arthurian England, 528 A.D., where he is befriended by Sir Sagramore le Desirous and gains power by judicious use of technology. He and Alisande, the King's niece, fall in love at first sight, which draws unwelcome attention from her fiancée Sir Lancelot; but worse trouble befalls when Hank meddles in the kingdom's politics.