c.450 to 651. Foundation of Northumbria
Bede notes that Northumbria was originally two separate kingdoms (HE, iii.1), Deira (north of the river Humber but south of the Tyne) and Bernicia (north of the Tyne). Genealogies survive for both Deira and Bernicia, taking both royal lines back to Woden. In the first half of the 7th century the two kingdoms became one, ruled by descendents of Ida of Bernicia until the second half of the 8th century (see entry on 759).
In the earliest dated reference to a member of either royal family, Bede notes that Ida took power in 547 and ruled for twelve years (HE, v.24). However, comments attached to earlier members of the genealogies of both Bernicia and Deira suggest at least legendary beginnings back in the 5th century. For the Bernicians, a 9th-century manuscript adds to a report of Ida of Bernicia's accession in 547 that Ida's grandfather Oessa was the first to arrive in Britain (Dumville, "Chronicle-fragment", p.314). A rough guess at two generations back from 547 would put Oessa's arrival towards the end of the 5th century. The Deirans claimed an even earlier beginning: the Historia Brittonum's version of the genealogy of the Deirans (?61) states that Soemel, the great-great-great-grandfather of Ælle of Deira (who was king in 597) separated Deira from Bernicia. Five generations from Soemel to Ælle would probably put this division in the mid-5th century, before the arrival of the English Bernicians, which would mean that Soemel separated Deira from British control (Dumville, "Origins", p.218). Though the exploits of Oessa and Soemel are not recorded before the 9th century and may well be fictitious, archaeological evidence does confirm that there were already Anglo-Saxons in Northumbria by the third quarter of the 5th century, long before Ida began to rule (Hines, pp. 26-7).
Whatever the arrangements were before Ida, he remains the first known Northumbrian king. There is a Bernician regnal list copied into an early manuscript of Bede's History, which lists the kings from Ida to Ceolwulf (729-37), and gives the number of years each reigned (see Hunter Blair). From this list we can deduce the following reigns for the kings from Ida to Æthelfrith, and these reign-dates are almost all that is known of the earliest Bernician kings:
Ida, 547-59
Glappa, 559-60
Adda, 560-8
Æthelric, 568-72
Theodric, 572-9
Frithuwald, 579-85
Hussa, 585-92
Æthelfrith, 592-616
There was probably a similar list for Deira, but since the Deiran line came to an end in the 7th century there would be less cause to preserve it, and all that remains is three entries in the Anglo-Saxon Chronicle: that in 560 Ælle succeeded to Northumbria and ruled for 30 years, that in 588 (not 590, as one might expect) Ælle died and Æthelric reigned for 5 years, and that in 593 Æthelfrith succeeded to Northumbria. This is clearly muddled, not only because Ælle should have died in 590 if he ruled for 30 years from 560, but also because Bede states that Ælle and Æthelfrith were both reigning north of the Humber when Æthelberht of Kent greeted the Roman missionaries in 597 (Bede, Chronica Maiora, entry 531, extracted at Miller, p.41). Bede's authority that Ælle was in power in 597 should be preferred over the Chronicle's assertion that Ælle died in 588 (and, implicitly, also in 590). The Chronicle entries are probably based on a regnal list which stated that Ælle reigned for 30 years, and then Æthelric reigned for 5 years, and then Æthelfrith took over Deira, but without knowing the date of Æthelfrith's conquest it is impossible to say when Ælle's reign should begin. (For a likely explanation of how the Chronicle arrived at Æthelfrith's accession in 593, and so put Æthelric's accession in 588 without recognizing the inconsistency with Ælle's accession in 560, see Miller, pp.46-7.) All we can say for certain about the Deiran kings before Edwin is that Ælle (Edwin's father) was ruling c.597.
The political situation in Northumbria was extremely fluid in the first half of the 7th century, with sometimes two separate countries, sometimes a united Northumbria under a Bernician ruler, and once a united Northumbria under a Deiran ruler. Æthelfrith of Bernicia (592-616; q.v.) was the first known ruler of all Northumbria, and Edwin of Deira succeeded him to the whole kingdom (616-33; q.v.). Shortly after the division of the kingdom on Edwin's death (see entry on 633) both kingdoms were reunited under Oswald of Bernicia (634-42); after Oswald's death in 642 there were again separate rulers until Oswiu of Bernicia ordered the killing of Oswine of Deira in 651. While there may have been sub-kings of Deira for the next thirty years or so, Oswine was probably the last independent king of a separate Deira, and so with hindsight we can say that Northumbria became a single kingdom under Bernician control in 651.
Though Northumbria may have been a single country from the mid-7th century, political fluidity remained something of a Northumbrian characteristic, as can be seen in the rapid changes of ruler (and dynasty) in the second half of the 8th century (see entry on 758), and the freedom with which the Northumbrians seemed to choose between English and Viking kings in the mid-10th century (see entry on 947-54).
J. Hines, "Philology, Archaeology and the adventus Saxonum vel Anglorum", Britain 400-600: Language and History, edd. A. Bammesberger and A. Wollmann (Heidelberg, 1990), pp.17-36
P. Hunter Blair, "The Moore Memoranda on Northumbrian History", in C. Fox and B. Dickins (edd.), The Early Cultures of North-West Europe (Cambridge: 1950), pp.245-57
D. Dumville, "A new chronicle-fragment of early British history", English Historical Review 88 (1973), pp.312-4
D. Dumville, "The Anglian collection of royal genealogies and regnal lists", Anglo-Saxon England 5 (1976), pp.23-50
D. Dumville, "The origins of Northumbria: some aspects of the British background", in S. Bassett (ed.), The Origins of Anglo-Saxon Kingdoms (London: 1989), pp.213-22
M. Miller, "The dates of Deira", Anglo-Saxon England 8 (1979), pp.35-61