He was the only son of Mary Queen of Scots and Lord Darnley. Upon the abdication of his mother in 1567 he was proclaimed king of Scotland. Until 1578, when he became king in fact, Scotland was in a turmoil because of a succession of ambitious regents. As king of Scotland, James pursued a policy against Presbyterians and Catholics, and succeeded in introducing a system of bishops. Upon the death of Elizaeth I in 1603, he became king of England. This union of crowns eventually led to the union of England and Scotland. His reign in England was marked by his partiality towards favourites, the sale of titles, and attempts to assert royal authority. He was characterised by Sully as "the wisest fool in Christendom". He was a witty, well-read scholar, but timorous and foolish in executive action.