Usiaslau Bryachislavich (also Vseslav also Usiaslau the sorcerer, ca. 1030-1101) was the most famous ruler of Polatsk. Saint Sophia Cathedral of that city (1066) is probably the most enduring monument in Belarus, which remained after his 60-years reign.

Upon his ascension to the throne of Polatsk in 1044, Usiaslau was the senior member of the Rurik Dynasty. Unable to secure the capital, which was held by Yaroslav's three sons, Usiaslau started pillaging neighbouring areas of Kievan Rus. In 1067 he laid siege to Pskov but was thrown back. A year later he pillaged and burnt Novgorod. After that he was defeated by the Yaroslavichi on the Niamiha river and treacherously captured during the peace talks.

During the Kievan rebellion of 1068, the crowd delivered him from prison, and the veche made him a grand duke. Feeling that his throne was insecure, Usiaslau escaped to Polatsk just 7 months later. After several years of complicated struggle with Iziaslav of Kiev, Vseslav finally secured Polatsk in 1071. During the last 30 years of his reign, his chief enemies were Vsevolod Yaroslavich and his son Vladimir Monomakh.

Like other Polatsk sovereigns, Usiaslau had a great reputation for sorcery and witchcraft. In moden Belarusian language he is known as Usiaslau the Sorcerer. Some people considered him a werewolf, as may be seen from the following lines of The Tale of Igor's Campaign:

In the seventh age of Troyan, Vseslav cast lots for the damsel he wooed. By subterfuge, propping himself upon mounted troops, he vaulted toward the city of Kiev and touched with the staff of his lance the Kievan golden throne. Like a fierce beast he leapt away from them at midnight, out of the white town, having enveloped himself in a blue mist.

Then at morn, he drove in his battle axes, opened the gates of Novgorod, shattered the glory of Yaroslav, and loped like a wolf to the Nemiga from Dudutki. On the Nemiga the spread sheaves are heads, the flails that thresh are of steel, lives are laid out on the threshing floor, souls are winnowed from bodies. Nemiga's gory banks are not sowed goodly - sown with the bones of Russia's sons.

Vseslav the prince judged men; as prince, he ruled towns; but at night he prowled in the guise of a wolf. From Kiev, prowling, he reached, before the cocks crew, Tmutorokan. The path of Great Sun, as a wolf, prowling, he crossed. For him in Polotsk they rang for matins early at St. Sophia the bells; but he heard the ringing in Kiev.

Although, indeed, he had a vatic soul in a doughty body, he often suffered calamities. Of him vatic Boyan once said, with sense, in the tag: "Neither the guileful nor the skillful, neither bird nor bard, can escape God's judgment.