Very nice rare stamp.
Bolesław I the Brave (967 – 17 June 1025), less often known as Bolesław I the Great (Polish: Bolesław I Wielki), was Duke of Poland from 992 to 1025, and the first King of Poland in 1025. As Boleslav IV, he was also Duke of Bohemia between 1002 and 1003. He was the son of Mieszko I of Poland by his wife, Dobrawa of Bohemia. According to a scholarly theory, Bolesław ruled Lesser Poland already during the last years of his father's reign. Mieszko I, who died in 992, divided Poland among his sons, but Bolesław expelled his father's last wife, Oda of Haldensleben, and his half-brothers and reunited Poland between 992 and 995.
Otto III (June/July 980 – 23 January 1002) was Holy Roman Emperor from 996 until his early death in 1002. A member of the Ottonian dynasty, Otto III was the only son of the Emperor Otto II and his wife Theophanu. Otto III was crowned as King of Germany in 983 at the age of three, shortly after his father's death in southern Italy while campaigning against the Byzantine Empire and the Emirate of Sicily. Though the nominal ruler of Germany, Otto III's minor status ensured his various regents held power over the Empire. His cousin Henry II, Duke of Bavaria, initially claimed regency over the young king and attempted to seize the throne for himself in 984. When his rebellion failed to gain the support of Germany's aristocracy, Henry II was forced to abandon his claims to the throne and to allow Otto III's mother Theophanu to serve as regent until her death in 991. Otto III was then still a child, so his grandmother, the Dowager Empress Adelaide of Italy, served as regent until 994.