Originally Posted by Iain
The British monarchy only came into being in 1707 and the first British Monarch was Queen Anne. Before that Scotland and England were independent countries and the Scottish monarchy was founded by King Fergus Mor who died in 501 AD. King Kenneth MacAlpin was the first king of a united Scotland (Scots and Picts) The monarchy of a United England was founded in 927 AD, 69 years after the death of King Kenneth MacAlpin.
Fergus Mor is a legendary King. Claiming that he was the founder of the Scottish monarchy is a bit of a stretch... Furthermore, while Fergus Mor may have been the first King of Dál Riata (or may not have; again legendary
), Dál Riata was not Scotland. Parts of it became parts of Scotland, and parts of it became parts of Ireland, but neither is a clear predecessor to the kingdoms that followed.
Cináed mac Ailpín, or Kenneth MacAlpin, became King of the Picts in 843, and is according to myth attributed with being the first King of Scotland. In the Pictish Chronicles go back to the legendary Drest I, who began his rule in 412, while other lists go back to Vipoig whose rule is attributed to having began in 312.
The Wessex conquest of England was completed in 927, under the first King of England Æthelstan, but much like Kenneth MacAlpin had his predecessors so did Æthelstan. Alfred the Great was King of the Anglo-Saxons - ruling all parts of England not conquered by the Danes - as early as 886, and 40 years earlier his grandfather, Egbert of Wessex, was briefly the first King to rule over all of England.
The Kingdom of Wessex, from which the Anglo-Saxon kings of England came from, can be traced back to Cerdic, in 519, although much like with Kenneth MacAlpin there is a degree of myth around Cerdic's life. None of the Anglo-Saxon kingdoms predate the 5th century (which makes sense, as the Anglo-Saxon conquest/migration occurred in the 5th century).
The Welsh, of course, have the Kingdom of Dyfed, which has its legendary origins in King Anwn, around 357.