Quoted from Wikipedia, article titled Borivoj I, Duke of Bohemia:

Borivoj I (c. 852 - c. 889) was the first historically-documented Duke of Bohemia (c. 870-c. 889) and founder of the Premyslid dynasty.
As the head of the Premyslids who dominated the environs of present-day Prague, Borivoj declared himself kníže - in Latin dux, which means sovereign prince - around the year 870 A.D. His title was later translated by German scholars as "duke" of the Bohemians (Czechs). Although the German dukes of the era held the same title, the meaning of his title was in fact completely different. In contrast to the German dukes, the Czech dux denoted a sovereign ruler. Borivoj was recognised as such around 872 by his overlord Svatopluk I of Great Moravia, who dispatched Bishop Methodius to begin the conversion of the Bohemian Slavs to Christianity. Borivoj and his wife Ludmila were baptised by Methodius (probably in 883), and the latter became an enthusiastic evangelist, although the religion failed to take root among Borivoj's subjects.
In the years 883/884 Borivoj was deposed by a revolt in support of his kinsman Strojmír. He was restored in 885 only with the support of his suzerain Svatopluk of Moravia. When Borivoj died about 4 years later, his sons still minors, Svatopluk took over the rule of Bohemia himself.
As with most of the early Bohemian rulers, Borivoj is a shadowy figure; exact dates for his reign and vital statistics cannot be established. Nonetheless, several major fortifications and religious foundations are said to have dated from this time. In old Czech legends he is said to have been son of a Bohemian prince named Hostivít.

• Married: BET 874 AND 875 ²

1. VRATISLAV I OF BOHEMIA b: 888
2. Spytihnev I of Bohemia b: 875

1. Author: Brian C. Tompsett
   Title: University of Hull
   Note:
   Source Medium: Electronic
   
   Page: http://www.dcs.hull.ac.uk/cgi-bin/gedlkup/n=royal?royal07188
2. Author: Charles Cawley
   Title: Foundation for Medieval Genealogy; http://fmg.ac/Projects/MedLands/index.htm
   Note:
   This database has undergone major changes and it is possible that this citation will not take you to what is now the correct location.
   Page: Bohemia, Chapter 1