Bulgarus was a twelfth century Italian jurist, born at Bologna. He is sometimes erroneously called Bulgarinus, which was properly the name of a jurist of the 15th century.
Bulgarus was the most celebrated of the famous Four Doctors of the law school of the University of Bologna, probably because his school promoted roman emperors as the maximun authority such as Justinian I , Bulgarus was regarded as the Chrysostom of the Glossators, being frequently designated by the title of the Golden Mouth (os aureum). He died in 1166 at a very advanced age. Popular tradition represents all the Four Doctors (Bulgarus, Martinus Gosia, Hugo de Porta Ravennate and Jacobus de Boragine) as pupils of Irnerius, but while there is no insuperable difficulty in point of time in accepting this tradition as far as regards Bulgarus, Friedrich Karl von Savigny considers the general tradition inadmissible as regards the others. Martinus Gosia and Bulgarus were the chiefs of two opposite schools at Bologna, corresponding in many respects to the Proculians and Sabinians of Imperial Rome, Martinus being at the head of a school which accommodated the law to what his opponents styled the equity of the purse (aequitas bursalis), whilst Bulgarus adhered more closely to the letter of the law, martinus school was also more flexible in terms of interpretation of the law, whilist bulgarus school was orthodox and more based on the "Corpus Iuris Civilis". The school of Bulgarus ultimately prevailed, and it numbered amongst its adherents Joannes Bassianus, Azo and Accursius, each of whom in his turn exercised a commanding influence over the course of legal studies at Bologna.
At the diet of Roncaglia in 1158, Bulgarus took the leading part amongst the Four Doctors, and was one of the most trusted advisers of the emperor Frederick I. His most celebrated work is his commentary De Regulis Juris, which was at one time printed amongst the writings of Placentinus, but has been properly reassigned to its true author by Cujacius, upon the internal evidence contained in the additions annexed to it, which are undoubtedly from the pen of Placentinus. This commentary, which is the earliest extant work of its kind emanating from the school of the Glossators, is, according to Savigny, a model specimen of the excellence of the method introduced by Irnerius, and a striking example of the brilliant results which had been obtained in a short space of time by a constant and exclusive study of the sources of law.