Lohengrin
2 of the 7 encyclopedias on this shelf carry an entry for Lohengrin. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
the hero of an old High German poem, written in the end of the 13th century. He was the son of Parzival, and a knight of the Grail. At King Arthur's command he was taken by a swan through the air to Mainz, where he fought for fo Elsa, daughter of the Duke of Brabant, overthrew her persecutor , and and married the lady. Then he accompanied the emperor to fight against the Hungarians, and subsequently warred against the Saracens. On his return home to Cologne, Elsa, contrary to his prohibition , persisted in asking him about his origin. After being asked a third time he told her, but was at the same time carried away by the swan back to the Grail. Rückert's edition (1857) of the poem is the best. The poem is a continuation of Wolfram von Eschenbach's " Parzival." Wagner made it the subject of his great opera, "Lohengrin" (1848).
Aiton's Encyclopedia (1910)
lo'en-grin, in German legend, the knight of the swan. He was the son of Parzival. Lohengrin is taken to Antwerp in a boat drawn by a swan. Here he weds a princess on condition that she shall never ask his name. She breaks her word and Lohengrin is borne away by the swan. The poem Parzival, written early in the thirteenth century by Eschenbach, mentions Lohengrin. In the latter half of the same century a poem called Schwanritter (Knight of the Swan) telling the story of Lohengrin, was written by Konrad von Wurzburg. Still another poem recounting the same legend was written in 1290 by an unknown Bavarian author. Wagner used the story as the subject for his great opera, Lohengrin.