Monk, scholar, theologian, and linguist (born Salonika, Greece, 827; died Rome, February 4, 869). With his brother Methodius he is credited with inventing the Glagolitic alphabet a precursor to the Cyrillic alphabet. The two convinced the Pope that the Slavs needed a Bible in their own language. He and his brother taught the alphabet as missionaries in Moravia.
Sorry I can not parse this:
His work was later transmitted by his pupils who made the journey back from Moravia to Bulgaria. Cyril, however, did not invent the alphabet on Bulgarian territory.
Cyril was canonized as a saint by the Orthodox Church and is also called "apostle of the Slavs".
Text to integrate from Schaff-Herzog Encyc of Religion:
1. Early Life of Cyril
Of the two "Apostles to the Slavs," Cyril (originally named Constantine) died in 869; Methodius, in 885. They were the sons of a subordinate military officer named Drungarius, born at Thessalonica, of Greek descent, but acquainted with Slavonic. The Vita Cyrilli has a marked preference for the number seven; according to it, Cyril or Constantine was the youngest of seven brothers, at seven years of age gave himself to the pursuit of heavenly wisdom, at fourteen was left an orphan. An influential official, possibly the eunuch Theoctistes, brought him to Constantinople. Photius is said to have been among his teachers; Anastasius mentions their later friendship, as well as a conflict between them on a point of doctrine. After the completion of his education Cyril took orders, and seems to have held the important position of chartophylax, or secretary to the patriarch and keeper of the archives, with some judicial functions also. After six months' quiet retirement in a monastery he began to teach philosophy and theology. In this period may fall his controversy with the deposed iconoclast patriarch John. The Vita also speaks of a journey into Mohammedan territory, and discussions with the inhabitants; and precisely at this time the difference between Christianity and Mohammedanism had become more sharply marked. The Vita connects his anti-Jewish polemics with his mission to the Chazars, a Finnish-Turkish tribe on the Sea of Azof under a Jewish king who allowed Jews, Mohammedans, and Christians to live peaceably side by side. It is uncertain how far we may trust the account of this journey, undertaken at the emperor's bidding; but Dummler has pointed out that the description of perils incurred from the Hungarians corresponds closely to what is known from other sources of their activity in those regions at this exact time. According to the Vita, Cyril found at Cherson an opportunity to learn the Hebrew and Samaritan languages, and, according to the Italian Legenda, also that of the Chazars. Anastasius says that he described his discovery of the bones of Saint Clement in a Storiola, a Sermo declamatorius, and a Hymnus, the first two of which Anastasius translated into Latin. Since Cyril, out of modesty, omitted to mention his own name, it may be inferred that the account extant in Slavonic, but no doubt originally Greek, comes from one of these works, probably from the Sermo declamatorius. The statement that Methodius accompanied him on the mission to the Chazars is probably a later growth. Methodius, a man of great practical energy, had already acquired a position of political importance, presumably the governorship of the Slavonian part of the empire; later, he became abbot of the famous monastery of Polychron.
2. Mission to the Slavs.
But both brothers were now to enter upon the work which gives them their historical importance. An independent Slavonic principality had been established by Rostislav, duke of Moravia; and to maintain this independence it was necessary to assert also the ecclesiastical independence of his state, which had been, at least externally, Christianized from the German side. Hauck accepts the statement of Theotmar that Rostislav expelled the Teutonic clergy at the beginning of his contest with the Franks. He then turned to Constantinople to find teachers for his people. It is obvious that the opportunity to extend Byzantine influence among the Slavs would be there; and the task was entrusted to Cyril and Methodius. Their first work seems to have been the training of assistants. The assertion that Cyril now undertook his translation of part of the Bible contradicts the statement of the Legenda that it had already been made before his undertaking of the Moravian mission; and the oldest Slavonic documents have a southern character. Cyril is designated by both friends and opponents of contemporary date as the inventor of the Slavonic script. This would not exclude the possibility of his having made use of earlier letters, but implies only that before him the Slavs had no distinct script of their own for use in writing books. The so-called Glagolitic script can be traced back at least to the middle of the tenth century, possibly even into the ninth; it presupposes a man of some education as its originator, and is evidently derived principally from the Greek, but also partly from the Latin cursive. The Cyrillian script is undoubtedly later in origin, and apparently was first used in Bulgaria. It is impossible to determine with certainty what portions of the Bible the brothers translated. Apparently the New Testament and the Psalms were the first, followed by other lessons from the Old Testament. The Translatio speaks only of a version of the Gospels by Cyril, and the Vita Methodii only of the evangelium Slovenicum; but this does not prove that 'Cyril did not translate other liturgical selections (see BIBLE VERSIONS, B, XVI., § 1). The question has been much discussed which liturgy, that of Rome or that of Constantinople, they took as a source. Since, however, the opposition objected only to the liturgical use of the Slavonic language, not to any alleged departure from the Roman type of liturgy, it is probable that the Western source was used. This view is confirmed by the "Prague Fragments" and by certain Old Glagolitic liturgical fragments brought from Jerusalem to Kief and there discovered by Saresnewsky-- probably the oldest document for the Slavonic tongue; these adhere closely to the Latin type, as is shown by the words "mass," "preface," and the name of one Felicitas. In any case, the circumstances were such that the brothers could hope for no permanent success without obtaining the authorization of Rome.
3. Appeal to Rome.
Accordingly, they went to Rome after three and a half years of labor, passing through Pannonia, where they were well received by the chieftain Kozel. The account of a discussion in Venice on the use of Slavonic in the liturgy is doubtful. But there is no question of their welcome in Rome, due partly to their bringing with them the relics of Saint Clement; the rivalry with Constantinople, too, as to the jurisdiction over the territory of the Slavs would incline Rome to value the brothers and their influence. The learning of Cyril was also prized; Anastasius calls him not long after "the teacher of the Apostolic See." The ordination of the brothers' Slav disciples was performed by Formosus and Gauderic, two prominent bishops, and the newly made priests officiated in their own tongue at the altars of some of the principal churches. Feeling his end approaching, Cyril put on the monastic habit and died fifty days later (Feb. 14, 869). There is practically no basis for the assertion of the Translatio (ix.) that he was made a bishop; and the name of Cyril seems to have been given to him only after his death.