May 2 is the traditional Church Holiday of Borisovden - everyone having the name of Boris and all the derivatives: Borislav, Borislava, Boryana celebrate their name day.
That day was originally celebrated in commemoration of one of the greatest Bulgarian rulers - Knjaz Boris I-Mikhail, canonized as a saint by the Bulgarian Orthodox Church, and May 2nd commemorates the day of his death. Knjaz Boris I-Mikhail was a remarkable ruler and the converter of the Bulgarian nation to Christianity. During his 37-year-reign (from 852 up to 889 A.D.) he managed to undertake considerable changes in political and spiritual life, leaving a significant cultural and historic impact.
The very powerful-then Bulgaria, being still a pagan state run by Khans, was not respected by the rest of the Christian Europe, which considered it as being unequal to their culture and manners. In 864, Khan Boris converted himself, accepting the new name of Boris I -Mikhail (which was the name of the then Byzantine Emperor, who served as his godfather) and the European title of Knjaz, and converted his whole nation to Christianity, which was declared the official religion of the state of Bulgaria, and all pagan beliefs and rituals were severely persecuted, even if performed by people closest to the Knjaz.
Knjaz Boris I-Mikhail built numerous churches and monasteries and fought for a Christian Church independent from Byzantine. One of the most essential results of his cultural policy is the introduction of the old Bulgarian language and writing in the church services and in political life, and also the creation of the first Bulgarian literacy and educational centers. He gave a wholehearted reception in the capital city of Pliska to Cyril and Methodius's disciples Kliment (Clement), Naum and Angelarius, and created favorable conditions for popularizing the Bulgarian language in literary and religious activities.
In 889 he voluntarily left his throne to retire in the monastery near the large basilica of Pliska. He broke his retirement twice - first to crush the uprising of the paganism supporters led by his own son Vladimir Rassate (whom he blinded and sent to a dungeon), and the second time - to lead his army against the Madzhars that had entered Bulgarian territories. Knjaz Boris I-Mikhail died on May 2, 907. His son, Tsar Simeon the Great (893-927), is considered to be the true successor of his wise policy.
Info: Bulgarian Rulers (Bulgaria.com)