Austrian-born language scholar of astonishing productivity in classical and medieval Latin, Germanic, and Celtic studies who produced the monumental Altceltischer Sprachschatz, 3 vol. (1891–1913; “Old Celtic Vocabulary”).

One of Holder's first major efforts was a two-volume edition of Horace (1864–69), prepared in collaboration with the German classical scholar Otto Keller. The chief librarian of the court and national library in Karlsruhe (1870–1916), he worked in four main fields of research. His editions of Latin authors include Tacitus (1882), Julius Caesar (1882, 1898), Avienus (1887), and works of Cicero, Seneca, and later writers. From ancient Greek and Roman works he assembled the highly useful compilation of Celtic names and glosses in his Sprachschatz. His Germanic research produced Germanische Alterthümer (1873; “Germanic Antiquities”), part of a grammar of Old German, and editions of many texts, including Beowulf (1882–84), Saxo Grammaticus (1886), and Bede (1890). His medieval Latin studies resulted in the catalog Die Reichenauer Handschriften, 3 vol. (1906–18; “The Reichenau Manuscripts”).