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The Ohnsorg Theater in Hamburg, Germany is a stage run after the British system of repertory theatre with up to six produced plays per season. Plays are exclusively performed in Platt and play a major role in spreading the knowledge and, in recent times, renewed appreciaton of this language. Exceptions in Hochdeutsch are only made for television broadcasts. Founded in 1902 by Dr. Richard Ohnsorg (1876–1947), these broadcasts on the regional NDR network for Northern Germany and on the nationwide ARD network have made the theatre and its former main star Heidi Kabel popular in many parts of Germany and beyond.
Although famous for its comedies, most of them set in the typical environment of Northern German farmers, fisher men or merchants from Hamburg, the theatre also performs more serious works of traditional literature and musical theatre as well as adaptations in Platt of international material such as the stage version of Stephen King's Misery and original plays such as Tennessee Williams's Cat on a Hot Tin Roof, Robert Thomas's 8 Women, Willy Russell's Shirley Valentine, Lawrence Roman's Alone Together or Shakespeare's A Midsummer Night's Dream. 
The theatre was founded by Dr. Richard Ohnsorg in 1902 as Dramatische Gesellschaft Hamburg, with the stated purpose of providing a stage on which plays in Platt could be performed. This was often not possible in other theatres, since platt was generally considered to be a sign of low social rank and rather boorish back then despite the fact that Platt was also spoken in the wealthy and educated circles of Hamburg's merchants and shipowners. 
Plays, some originally written in Platt, others translated from High German and other languages, were performed in cramped circumstances and various locations. In 1920, its name was changed to Niederdeutsche Bühne Hamburg e. V.. The letters e. V. stand for Eingetragener Verein, which, under German law, can only be run by volunteers. Thus, the company now had to rely on volunteers to stage any production.
In 1936, the company moved into the former Kleine Lustspielhaus on the Großen Bleichen. The NSDAP was sympathetic to the company's aim to stimulate local culture; the brand comedy delivered by Ohnsorg, and his company was popular. After the war, the theatre was renamed the Richard Ohnsorg-Theater (1946), and since 1954 its plays are broadcast by the NDR. Especially during the 1960s and 70s its productions made the cast hugely popular, especially its main star Heidi Kabel who remained with the theatre until her retirement in 1997.
The theatre moved into a new larger playhouse in 2011, which was built in the listed Bieberhaus close to the Deutsches Schauspielhaus and Hamburg Hauptbahnhof. A part of the square in front of the theatre was renamed after Heidi Kabel right before the theatre moved and a memorial in her honor was erected next to the theatre's entrance.
- Gerd Spiekermann: 100 Jahre Ohnsorg Theater, Die Hanse – Sabine Groenewold Verlage, Hamburg 2002, ISBN 3-434-52600-5
- Home Page of the Ohnsorg Theater (in German)
- Peter Schmachthagen: Sprechen Sie Hamburgisch - Vol. I, Axel Springer Verlag/Hamburger Abendblatt, Hamburg 2009, ISBN 978-3-939716-26-6
- Peter Schmachthagen: Sprechen Sie Hamburgisch - Vol. II, Axel Springer Verlag/Hamburger Abendblatt, Hamburg 2010, ISBN 978-3-939-716-31-0