All his acts relate that he suffered under Diocletian at Nicomedia. Joseph Assemani6 shows, from the unanimous consent of all churches, that he was crowned on the 23rd of April. According to the account given us by Metaphrastes, he was born in Cappadocia, of noble Christian parents. After the death of his father he went with his mother into Palestine, she being a native of that country, and having there a considerable estate, which fell to her son George. He was strong and robust in body, and having embraced the profession of a soldier, was made a tribune, or colonel, in the army. By his courage and conduct he was soon preferred to higher stations by the Emperor Diocletian. When that prince waged war against the Christian religion, St. George laid aside the marks of his dignity, threw up his commission and posts, and complained to the emperor himself of his severities and bloody edicts. He was immediately cast into prison, and tried, first by promises, and afterwards put to the question and tortured with great cruelty; but nothing could shake his constancy. The next day he was led through the city and beheaded. Some think him to have been the same illustrious young man who tore down the edicts when they were first fixed up at Nicomedia, as Lactantius relates in his book, On the Death of the Persecutors, and Eusebius in his history.
According to EWTN:
Born 939 of a noble Bohemian family; died 997. He assumed the name of the Archbishop Adalbert (his name had been Wojtech), under whom he studied at Magdeburg. He became Bishop of Prague, whence he was obliged to flee on account of the enmity he had aroused by his efforts to reform the clergy of his diocese. He betook himself to Rome, and when released by Pope John XV from his episcopal obligations, withdrew to a monastery and occupied himself in the most humble duties of the house. Recalled by his people, who received him with great demonstrations of joy, he was nevertheless expelled a second time and returned to Rome. The people of Hungary were just then turning towards Christianity. Adalbert went among them as a missionary, and probably baptized King Geysa and his family, and King Stephen. He afterwards evangelized the Poles, and was made Archbishop of Gnesen. But he again relinquished his see, and set out to preach to the idolatrous inhabitants of what is now the Kingdom of Prussia. Success attended his efforts at first, but his imperious manner in commanding them to abandon paganism irritated them, and at the instigation of one of the pagan priests he was killed. This was in the year 997.