Bogusà Âaw Radziwià Âà  (; 3 May 1620 – 31 December 1669) was a Polish princely magnate and a member of the Polish-Lithuanian szlachta, or nobility. He was of the Radziwià Âà  magnate family. By birth he was an Imperial Prince of the Holy Roman Empire. He was a descendant of the famous knight, Zawisza the Black. Following the death of Janusz Radziwià Âà Â, he briefly served as Grand Hetman of Swedish Lithuania.
Born of the mightiest and highest resident family of the Grand Duchy of Lithuania (as well as a blood descendant of King Casimir IV of Poland, and KÃÂstutis and Vytautas, monarchs of Lithuania), Radziwià Âà  was the owner of Birà ¾ai, Dubingiai, Sà Âuck, and Kopyta, the great Standard-bearer of Lithuania since 1638, the Master of the Stables of Lithuania since 1648, and the Starost of Bar. Radziwià Âà  was Governor of the Duchy of Prussia (Brandenburg-Prussia) (generalny gubernator Prus KsiÃ à ¼ÃÂcych) since 1657.
From 1637 to 1648 Radziwià Âà  studied abroad, in Germany, Netherlands, England, and France.
For several decades, the interests between the Radziwià Âà  family and the PolishâÂÂLithuanian Commonwealth had begun to drift apart, as Radziwà Âà  were less satisfied with the magnate status of the family and its immense wealth and began craving more political power.
Together with his cousin Janusz Radziwià Âà  in 1654 during The Deluge, or Swedish invasion of Poland, Bogusà Âaw Radziwià Âà  began negotiations with King Charles X Gustav of Sweden aimed at breaking the Commonwealth and the PolishâÂÂLithuanian union. They signed a treaty according to which the SwedishâÂÂLithuanian union was founded and the Radziwià Âà Âs 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).
The Swedish defeat and eventual retreat from the territories of the Commonwealth abruptly ended the plans of Janusz and Bogusà Âaw. The former died at Tykocin Castle besieged by forces loyal to the Commonwealth, while Bogusà Âaw retreated with his forces to Prussia, where he supported Frederick William, Elector of Brandenburg, against the Polish king. In the Battle of Prostki on 8 October 1656, Bogusà Âaw's forces were decimated by the Commonwealth forces under Hetman Wincenty Korwin Gosiewski. Radziwià Âà  himself was captured by the Tatars, who initially enslaved him and wanted to transport him to Crimea. After fierce discussions with the Tatar commanders, he was handed over to Gosiewski.
From October to 10 December 1659, he participated in the successful blockade and capture of Strasburg in conjunction with a PolishâÂÂLithuanian force.
Boguslaw married Anna Maria Radziwià Âà Â, the only daughter of his relative and collaborator, the late prince Janusz. In turn, this couple had only one surviving child, a daughter, Ludwika Karolina Radziwià Âà Â. Both Bogusà Âaw's and Janusz's lines of the Radziwià Âà  family became extinct by the next generation.
In Poland it is believed that Bogusà Âaw's and Janusz's only lasting achievement was to tarnish the Radziwià Âà  family name for years to come with their treason, eclipsing the deeds of other Radziwià Âà Âs like Michaà  Kazimierz Radziwià Âà Â, who fought for the Crown and the Commonwealth against the Swedes. Bogusà Âaw 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.
Bogusà Âaw died in exile in Königsberg in Brandenburg-Prussia. He was the last Calvinist male member of his family. His estates and the task to protect the Polish Reformed Church passed to his only daughter, Princess Ludwika Karolina.