James VI and I
The first monarch to occupy the thrones of both England and Scotland - with the acceptance of both populations - was James Stuart (1566-1625), the son and heir of Mary Queen of Scots. He was one of many of his family to have ruled Scotland, and two accepted as Kings of England. So he was James VI ('the sixth') of Scotland, and James I ('the first') of England. As he was King of Scotland before he inherited the English throne from Elizabeth I in 1603, it is proper to call him James VI and I in that order. In 1604, however, he issued a proclamation saying that "Wee ... take and assume unto Us in maner and forme hereafter expressed, The Name and Stile of KING OF GREAT BRITTAINE" (Larkin, James F. and Hughes, Paul L. (1973) Royal Stuart Proclamations, vol. 1 [on-line] http://www.heraldica.org/topics/britain/britstyles.htm#1604, accessed 02-07-09). There is a tendency in England to refer to him simply as James I, which he was, of Great Britain. In attempting greater formality, English writers sometimes make the error of calling him '
James I and VI': avoid this mistake. If you are writing only about English history, or about Britain as a whole, James I is correct, as is James VI when writing only about Scottish history. In writing about the politics of the period, it may often be better to call him James VI and I.
James became King of Scotland in 1567, when only thirteen months old, on the abdication of his mother; and of England in 1603, on the death of his cousin Elizabeth. He ruled both - separate - countries until his death in 1625. The adjective Jacobean is used to describe his reign, and the styles associated with it in furniture, literature, architecture and so on.