Christian Rudolph Wilhelm Wiedemann (7 December 1770 in Brunswick – 31 December 1840 in Kiel) was a German physician, historian, naturalist and entomologist. He is best known for his studies of world Diptera, but he also studied Hymenoptera and Coleoptera, although far less expertly.
 Wiedemann’s father, Conrad Eberhard Wiedemann (1722–1804) was an art dealer and his mother, Dorothea Frederike (née Raspe) (1741–1804) was the daughter of an accountant in the Royal Mining Service and also interested in the arts.
 After his education in Brunswick, he matriculated in 1790 to the Faculty of Medicine at the University of Jena where he was a contemporary of the poet Friedrich von Hardenberg.
 While attending university, Wiedemann, was one of the many pupils of Johann Friedrich Blumenbach, and travelled to Saxony and Bohemia. He obtained his doctoral degree in 1792 with a thesis entitled  Dissertatio inauguralis sistens vitia gennus humanum debilitantia. He then went to England to increase his knowledge of mineralogy.
 Appointed Professor of Anatomy at Brunswick’s Collegium Carolinum in 1794, his inaugural address was about a medical condition observed in a boy at Llandeilo, Wales. It was titled Über das fehlende Brustbein, English “On the missing breastbone”.
 In 1796 he married Luise Michaelis, the daughter of Johann David Michaelis, an Orientalist. They would raise the two sons of Luise's brother, who died in a cholera epidemic. The couple had nine children of their own, two dying in infancy.
 He was later appointed Lecturer in his specialist field obstetrics
 In the late 17th century, there was a movement, based in Brunswick, to establish German as a scientific language. Able to read Latin, English, French and Italian, Wiedemann found remunerative work as a translator.
 In 1801 he received a scholarship for study in Paris from the Duke of Brunswick. Here he studied obstetrics and natural history and met Georges Cuvier, amongst other zoologists.
 In 1802, he was, in addition to his other medical appointments, made Professor of Obstetrics at the College of Anatomy and Surgery and was nominated Privy Councillor at the court of the Duchy of Brunswick and Lüneburg.
 In 1804 he contracted syphilis which had serious effects in later years.
 In 1805 he became Professor of Medicine in Kiel (then in Denmark and part of the Duchy of Holstein) with the title Counsellor of Justice and, later Counsellor of State. These were difficult years for Denmark which had sided with France in the Napoleonic Wars against England (and her allies) to preserve her maritime empire. Money was a problem and Wiedemann used his own resources to set up the midwifery clinic proposed as one of his duties as professor.
 In 1811 he travelled south to Italy for his health.
 From around 1814 Wiedemann devoted much of his time to taxonomic entomology and in 1815, on a visit to Bonn to stay with his daughter Emma who had married Carl Theodor Welcker later a radical embroiled in the turbulent politics of the 1840s he travelled to Stolberg to meet Johann Wilhelm Meigen a, by then, well known entomologist through his important work on Diptera. Perhaps, not able to attend properly to his medical duties through ill health- he visited the spa town of  Bad Aachen in 1817- Wiedemann changed employment (to Pharmacology) and had several semi-honorary positions. With more time and sedentary, he prepared and studied insects and went on collecting trips for his health. He also gave lectures on entomology and natural history.
 Wiedemann’s most productive work on insects was accomplished in the 1820s. But when he attended a scientific meeting in Hamburg in 1830 this  too was drawing to a close. His eyesight was very poor and he had a succession of strokes.
 Wiedemann main natural history interest remained entomology but he was also interested in mineralogy and conchology. In 1827 his collections included 5,000 minerals and over 3,500 species of  Diptera.
 He is known to have visited Hamburg, Copenhagen and Berlin in these years but nothing is so far known of these trips although they  may well have been to further his insect studies.
 Wiedemann published the first monographs on “exotic” (non-European) Diptera.
He was the creator of the transitory review Archiv für Zoologie und Zootomie 1800-1806 (five volumes) 2,356 pages. Berlin and Brunswick and the Zoologisches Magazin (volumes 1-2) 1817-1823 749 pages. Kiel and Altona.
 Although he worked mainly on Diptera he also published descriptions of Coleoptera and (at least one) Hymenopteran.
 He was the successor to Johan Christian Fabricius as the author of descriptions of “exotic” that is non-European Diptera. Meigen worked only on the European species.
 His descriptions show clear advances, both over Fabricius and many of his contemporaries. A brief Latin diagnosis, a fuller detailed description in German, the sex of the specimen, locality details, a reference to the collection in which the specimen was to be found and, sometimes, the name of the collector.
 In Brunswick, then an important centre for entomology Wiedemann worked with Johann Christian Ludwig Hellwig and Johann Karl Wilhelm Illiger setting new standards for descriptions (uniform terminology for structures and colour) and for nomenclature, especially in regard to the avoidance of synonyms by proper research of pre-existing literature. He was critical of Fabricius in this respect, although honouring him as a great entomologist.
 In Aussereuropäische Zweiflügelige Insekten he described 1000 new and redescribed 500 old (mainly Fabrician) species. This work, supplemental to Meigen followed Meigen in introducing many new genera. He could have gone further than he did with “exotic” genera. He introduced too few of these but the full extent of diversity of world Diptera was not then apparent. The work includes descriptions of Diptera collected by Ferdinand Deppe in Mexico.
 Wiedemann, in his studies of the Fabrician) species was careful to consider only Fabricius specimens identified by their labels in Fabricius’ hand. This is at the core of the modern concept of type specimens.
 He made his studies as comprehensive as possible, studying the collections of Wilhelm Von Winthem and Bernt Wilhelm Westermann and studied the collections in Copenhagen, Berlin, Frankfurt, Kiel, Leiden and Vienna. He also studied Thomas Say’s borrowing these from the Philadelphia museum. He was unable to study the Linnean and the Fabricius types (both in London) or visit Paris.
 Wiedemann's published work on entomology was almost entirely descriptive and notable for its accuracy.
 Wiedemann's collection of Diptera and Hymenoptera was taken over by Wilhelm von Winthem who presented part to the Natural History Museum, Vienna (Naturhistorisches Museum, Wien) the rest to  the Senckenberg Museum in Frankfurt, The Zoological Museum, University of Copenhagen (Zoologisk Museum, Københavns Universitet).
Collection contents online 
 The Wiedemann Range in Greenland was named after him.