Frederick I von Büren of Hohenstaufen, Duke of Alsace and Swabia

  Research Notes:

From Wikipedia - Frederick I, Duke of Swabia :

Frederick I von Büren (1050 -July 21 , 1105 ) was Duke of Swabia from 1079 to his death. He was the first ruler of Swabia of the House of Hohenstaufen . He was the son of Friedrich von Büren and Hildegard.
In 1089, Frederick married Agnes of Germany , daughter of Henry IV, Holy Roman Emperor . They had several sons and daughters, amongst whom were:
Frederick II of Swabia (1090-1147), the father of Frederick Barbarossa
Conrad III, king of Germany (1093-1152)

See also
Dukes of Swabia family tree

Source
Ancestral Roots of Certain American Colonists Who Came to America Before 1700 by Frederick Lewis Weis, Line 45-24

Frederick married Agnes of Germany, daughter of Henry IV Holy Roman Emperor and Bertha of Savoy, in 1089. (Agnes of Germany was born in 1072 and died on 24 Sep 1143.)

  Marriage Notes:

Ancestral Roots has m. 1086/7 (engaged 24 Mar 1079).
Wikipedia has m. 1089