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Kasper D(o)enhoff (German: Kaspar von Dönhoff, Polish: Kacper Denhoff, 1587 - 1645) was a Baltic-German noble (Reichsfürst) of the Holy Roman Empire and a noble (szlachcic), a Voivode of the Dorpat Voivodeship; courtier and a diplomat at the court of the kings of the Polish-Lithuanian Commonwealth.
Polish noble (szlachcic) of Denhoff Coat of Arms, voivode of Dorpat (1627-1634), since 1633 Count of the Holy Roman Empire (with Ernst and Gerhard Dönhoff), voivode of Sieradz (1634-1645), court marshal of the Queen (from 1639), starost of Wieluń, Lauenburg (Lębork), Radomsko, Bolesławiec, Sokal, Małoszyce, Sobowidze, Klonowo. In Holy Roman Empire, noble (Reichsfürst), count (from 1635), prince (from 1637) and court marshal.
The member of the Westphalian, Prussian and Baltic-German Family von Dönhoff  (e.g. Marion Dönhoff) Kasper became a military commander (rotmistrz of reiters), a favourite of king Sigismund III Vasa (after his conversion to Catholicism) and one of the most prominent members of the so-called 'court faction', advocating the strengthening of the monarch's power.
As a courier of the House of Vasa king Władysław IV Vasa he was sent with a diplomatic mission to request a marriage of Archduchess Cecilia Renata of Austria, daughter of Ferdinand II, Holy Roman Emperor to Wladyslaw. The mission was successful and Kasper also received noble titles from the Holy Roman Emperor.
Kaspar Dönhoff was a relative newcomer to the 'magnate' ruling elite of the Polish-Lithuanian Commonwealth, but he laid the foundations of his family's fortune.
Legacy as builder-owner
He was influential and wealthy, which enabled him to found several interesting construction projects, mostly in the Sieradz voivodeship. His first undertaking of that sort was the transformation of a mediaeval castle in Bolesławiec (of which he was the starost) on the Prosna River into a comfortable residence surrounded with an 'Italian garden'. Later he sponsored the construction of a magnificent baroque castle in Kruszyna around 1630. Kruszyna castle was the last residential complex erected in Poland that had been planned around a renaissance internal yard, but its grand front yard and garden marked a fully baroque layout. Kruszyna became Denhoff's main residence; but as it was located rather far from the capital of Warsaw, in 1636 he bought an estate much closer to the capital, in Ujazd, where he pulled down an old castle and built another palace, probably also surrounded with a garden. Towards the end of his life he founded a domed chapel as a necropolis for himself and his family in the Jasna Góra sanctuary in Częstochowa; that undertaking was completed by his descendants. Despite being the owner of several castles, he lived most often in a wooden manor (dworek szlachecki) near the King's residence in Warsaw. 
- Son of Gerhard Dönhoff  (?-1598) and M. von Zweiffeln
- Brother of Ernst Magnus Dönhoff (voivode of Parnawa), Hermann Dönhoff and Gerhard Dönhoff  (1590-1648) (voivode of Pomorze)
- Married Anna Aleksandra Koniecpolska in 1620. They had four children: Aleksander Denhoff, Stanislaw Denhoff (?-1653), Zygmunt Denhoff, Anna Denhoff
- Stanisław Ernest Denhoff (1673-1728)
- ↑ Niesiecki, Kasper (1846) (in Polish). Herbarz polski Kaspra Niesieckiego. P.228: Waif. http://books.google.com/books?id=sGBJAAAAIAAJ&printsec.