Short answers, pulled from the story.
Saint George was executed by decapitation on the 23rd of April 303 at Diospolis, also known as Lydda, in Palestine. He was a soldier of Cappadocian Greek descent who refused to renounce his Christian faith during the Diocletianic Persecution.
England, Portugal, Georgia, Ethiopia, Bulgaria, Ukraine, Malta, Bosnia and Herzegovina, and the historical regions of Catalonia and Aragon have all claimed George as patron saint. The cities of Moscow and Beirut, as well as several other regions and organisations worldwide, also count him as a patron.
According to the legend codified in the 13th-century Golden Legend by Jacobus de Voragine, Archbishop of Genoa, George slew a dragon terrorising the Libyan city of Silene. The city had been sacrificing people by lot when its sheep supply ran out; George arrived as the king's daughter was to be sacrificed, killed the dragon with his lance, and refused any reward, urging the king to give treasures to the poor instead.
George appears in Islamic sources as a prophetic figure called Jirjis or Girgus, identified variously with the prophet Elijah and with al-Khidr, meaning the verdant prophet. Muslim legends describe him being martyred multiple times and resurrected each time, with one account by Ibn al-Athir comparing his death to the crucifixion of Jesus. Shrines attributed to George are visited by Muslims across the Middle East, including the monastery at Al-Khader near Bethlehem.
Saint George's Cross, the red cross on a white field, most likely originated in Genoa, which adopted George as patron and used the cross as its flag by the 12th century. Edward III of England began using the red-on-white cross in 1348, the same year he placed the Order of the Garter under George's patronage. The cross now forms the national flag of England and overlaps with Scotland's flag to produce the Union Jack.
The oldest surviving tradition of the legend is a Coptic manuscript discovered in 1964 in the ruins of the cathedral of Qasr Ibrim in Nubia, dated between 350 and 500. It names George's father as Gerontius from Cappadocia and his mother as Polychronia, a Christian who had George baptised in secret. The earliest Greek hagiography is a palimpsest identified by the Bollandist scholar Hippolyte Delehaye as dating to the 5th century.