SLEIDANUS, JOHANN. - He was the most celebrated annalist of the German Reformation, born probably in 1506 at Schleiden in the Eifel, of the Philippi family; he was educated at Liège; he seems to have studied at Cologne; the first reliable document concerning him is a letter from the summer of 1530 in which he shows himself an Erasmian humanist, with a warm admiration for Melanchthon, and discerns in the German religious revolution a sharp opposition to imperial policy.
From 1533 he remained for many years in France: he was in Paris with Johann Sturm (1534); in Nov. 1538 he enrolled for the licentiate in law at Orléans, and he stayed with Cardinal Jean du Bellay and his brother François until the death of Francis I. He was at Hagenau on a secret mission to Philip, Landgrave of Hesse, and there met with the leaders of the Lutheran movement. In 1544 he was to accompany Cardinal du Bellay to the Diet of Speyer, but they got only as far as Nancy; S. remained in Strasbourg and translated into Latin Bucer's Short Catechism. This marked him out to the Landgrave as a possible historian, all the more so since he had gathered material on the Schmalkaldic League. He was ambassador in England, where he was able to form friendships and gather news. He was at Trent from the spring of 1551 to Apr. 1552 as an envoy; in 1554 he was with Vergerio. In 1554-55 his major work was printed, De statu religionis et reipublicae Carolo V Caesare commentariorum libri XXVI, at Strasbourg, dedicated to Augustus, Elector of Saxony, and soon prohibited by the Emperor, attacked by Protestants and Catholics alike, because, according to Melanchthon, it recounted much that would better have been passed over in eternal silence. S. died on 31 Oct. 1556; in June he had published De quattuor summis imperiis libri III. His minor writings were collected in Opuscula, Hannover 1608.