Which monarch was responsible for creating the union jack?

The Union Jack was created under the reign of King James VI of Scotland and I of England. The flag was first adopted in 1606, following James's ascension to the English throne in 1603, symbolizing the union of the crowns of England and Scotland. The design combined elements of the crosses of St George for England and St Andrew for Scotland, and later, in 1801, St Patrick's cross was added to represent Ireland.