Bridei son of Beli, died 692 was king of Fortriu and of the Picts from 671 until 692. His reign marks the start of the period known to historians as the Verturian hegemony, a turning point in the history of Scotland, when the uniting of Pictish provinces under the over-kingship of the kings of Fortriu saw the development of a strong Pictish state and identity encompassing most of the peoples north of the Forth.

Bridei was probably brought up at the court of the Anglian kingdom of Northumbria, whose expansion had established it as the dominant power in northern Britain over the mid-7th century. His father was Beli, king of the British kingdom of Altclut, and his mother probably a daughter of Edwin of Northumbria, though his grandfather may have been the earlier Pictish king Nechtan nepos Uerb.

Bridei's rise to power in Fortriu probably took place under the patronage of his kinsman King Ecgfrith of Northumbria, after Bridei's predecessor Drest son of Donuel was expelled from the kingship after leading a rebellion against Northumbrian domination in 671. Bridei established an expansionary policy however, and in a series of campaigns between 679 and 683 built a confederation of Pictish territories owing allegiance to him through alliance and conquest. This brought him into conflict with Ecgfrith, who led an army north into Pictish territory in 685, culminating in the Battle of Dun Nechtain, when Ecgfrith was killed and the Northumbrian army destroyed by Bridei's forces.

Bridei's victory at Dun Nechtain marked the end of Northumbrian overlordship over the Picts, the Gaels and many of the Britons; and saw him consolidate his extensive territorial control. The following period saw the conscious development of the idea of the Picts as a single people under a single ruler; this process continued under the later kingships of Bridei son of Der-Ilei and Naiton son of Der-Ilei, who were probably his grandchildren.

Before the Viking incursions that started in the late 8th century, the area of modern Scotland was divided between four main cultural and linguistic groupings: the Gaels of Dál Riata, the Britons, the Angles and the Picts, though identities and political groupings were in a constant state of flux and could often change among and between them. The Gaels occupied the west of modern Scotland north of the Firth of Clyde and were part of a Gaelic linguistic and cultural zone that included Ireland, from which it was separated only by the short sea crossing of the North Channel.

To the south a number of British kingdoms had developed in the aftermath of the withdrawal of the Roman Empire, including Altclut in the basin of the River Clyde, Rheged to the south around the Solway Firth, and the Gododdin to the east around Edinburgh. In the south east Bernicia had been established as a Germanic-speaking Anglian kingdom based around Bamburgh in modern North East England in the mid 6th century, and by 638 had captured Edinburgh and gained much of the territory of the Goddodin around Lothian. The Picts largely occupied the lands in the east of modern Scotland north of the Forth and were originally a diverse group of peoples defined at least in part by never having been Romano-British.

The territory of the Picts was divided into two parts by the Mounth – the chain of high mountains that runs almost to the North Sea near Dunottar – and the northern and southern parts of the Pictish territory were further divided into smaller territories referred to by the Northumbrian writer Bede as prouinciae, at least some of which are recorded as kingdoms. Most significant of these was Fortriu, which was located north of the Mounth around the Moray Firth, encompassing the areas around Forres and Inverness, and whose primary centre of royal power probably lay at Burghead, which was three times larger than any other enclosed site in Early Medieval Scotland.

Between 653 and 685 the Picts were under Anglian overlordship through a series of puppet kings, as the expansionary kingdom of Northumbria came to dominate much of northern Britain. The southern Pictish lands south of the Mounth may have formed an Anglo-Pictish province controlled from Fife, whose ruling family may have included the Northumbrian noble Beornhæth. A document written in Rome between 678 and 681 records the claim of the Northumbrian bishop Wilfrid to primacy over "all the northern part of Britain and of Ireland and the Isles which are inhabited by the races of Angles, Britons, Gaels and Picts". In 681 the Northumbrian bishop Trumwine was appointed "Bishop of the Picts", though the location of his see at Abercorn, in Northumbrian territory south of the Forth, suggests that Northumbrian control of Pictish territory north of the Forth might still have been seen as insecure.