Simeon was born in 864 or 865, as the third son of Knyaz Boris I of Krum's dynasty.
As Boris was the ruler who had Christianized Bulgaria in 865, Simeon has been a Christian all his life.
Because his eldest brother Vladimir had always designated heir to the Bulgarian throne, Boris had intended Simeon to become a high-ranking cleric, possibly Bulgarian archbishop, and had sent him to the University of Constantinople to receive theological education when he was thirteen or fourteen.
He had taken the name Simeon as a novice in a monastery there.
During the decade (from about 878 to 888) he spent in the imperial capital, he had received an excellent education and studied the rhetoric of Demosthenes and Aristotle.
He had also learned fluent Greek, to the extent that he is referred to as "the half-Greek" in Byzantine chronicles.
He is speculated to have been tutored by Patriarch Photios I of Constantinople, but this is not supported by any source.
Around 888, Simeon had returned to Bulgaria and settled at the newly established royal monastery of Preslav, where, under the guidance of Naum of Preslav, he has engaged in active translation of important religious works from Greek to Old Church Slavonic (Old Bulgarian), aided by other students from Constantinople.
Meanwhile, Vladimir had succeeded Boris, who had retreated to a monastery, as ruler of Bulgaria.
Vladimir has attempted to reintroduce paganism in the empire and possibly signed an anti-Constantinople pact with Arnulf of Carinthia, forcing Boris to reenter political life.
With the aid of loyal boyars and the army, Boris drives his dissolute son from the throne and has him blinded, unfitting him for rule.
He then convenes a council that confirms Christianity as the religion of the state and moves the administrative capital from Pliska to the Slavic town of Preslav to better cement the recent conversion.
The assembly also proclaims Bulgarian as the only language of state and church.
It is not known why Boris did not place his second son, Gavril, on the throne, but instead preferred Simeon.
Boris now retires permanently to monastic life, making generous grants to the Bulgarian Church and patronizing Slav scholarship.
