Sviatoslav I Igorevich (c. 942 – March 972), also spelled Svyatoslav, is a prince of Rus.

The son of Igor of Kiev and Olga, Sviatoslav is famous for his incessant campaigns in the east and south, which precipitate the collapse of two great powers of Eastern Europe—Khazaria and the First Bulgarian Empire; he also conquers numerous East Slavic tribes, defeats the Alans and the Volga Bulgars, and at times is allied with the Pechenegs and Magyars.

His decade-long reign over Rus' is marked by rapid expansion into the Volga River valley, the Pontic steppe and the Balkans.

By the end of his short life, Sviatoslav has carved out for himself the largest state in Europe, eventually moving his capital from Kiev (modern day Ukraine) to Pereyaslavets (modern day Romania) on the Danube in 969.

In contrast with his mother's conversion to Christianity, Sviatoslav remains a staunch pagan all of his life.

Due to his abrupt death in ambush, Sviatoslav's conquests, for the most part, are not consolidated into a functioning empire, while his failure to establish a stable succession leads to fratricidal feud among his sons, resulting in two of his three sons being killed.