(1620 – 1669) was a princely magnate and a member of the Polish-Lithuanian szlachta
, or nobility. He was of the Radziwiłł magnate
family. By birth he was an Imperial Prince of the Holy Roman Empire.
A descendant of the famous knight Zawisza Czarny.
Together with his cousin Janusz Radziwiłł in 1654 during The Deluge, or Swedish invasion of Poland, Bogusław Radziwiłł began negotiations with King Charles X Gustav of Sweden aimed at breaking the Commonwealth and the Polish–Lithuanian union. They signed a treaty according to which the Swedish–Lithuanian union was founded and the Radziwiłłs were to rule over two duchies carved up from the lands of the Grand Duchy of Lithuania (this was also confirmed in another treaty, the treaty of Radnot).
In Poland it is believed that Bogusław’s and Janusz’s only lasting achievement was to tarnish the Radziwiłł family name for years to come with their treason, eclipsing the deeds of other Radziwiłłs like Michał Kazimierz Radziwiłł, who fought for the Crown and the Commonwealth against the Swedes. Bogusław is the archvillain in a novel by Henryk Sienkiewicz, The Deluge, which is mandatory school reading in Poland, and is also the basis for a very popular eponymous film.