Bulan, the Khazar ruler

The main source on Bulan is the 10th-century letter of the Khazar king Joseph to Hasdai ibn Shaprut of Córdoba. According to the letter, Bulan saw an angel in a dream, then invited Christian, Muslim and Jewish scholars to a debate and chose Judaism.

The date is disputed: some scholars place it in the mid-8th century, after the Arab-Khazar wars, others in the 9th century. In the Khazar Khaganate only the ruling elite adopted Judaism, while Muslims, Christians and followers of Tengri lived side by side among the people. The year given for his era is approximate.