Lindsey was an early medieval kingdom south of the Humber estuary, in roughly the area of north Lincolnshire. See sketch map for its approximate location. The name was recorded by Bede in his Ecclesiastical History, written in 731, as 'prouinciae Lindissi' or 'the province of Lindsey' (Book II Ch. 16). What do we know about its rulers?
The genealogy of the kings of Lindsey is given in the Anglian Collection, as follows:
--Anglian Collection genealogies, available online
Each king is given a patronymic derived from the name of his predecessor, e.g. Finn Godwulfing, Frithulf Finning, and so on. (I have missed the patronymics out of the list above for ease of reading). Presumably whoever compiled the genealogy believed, or wished to indicate, father-to-son succession. This may have been accurate, or it may result from a scribe misinterpreting a king list as a genealogy, or a bit of both.
There is a village called Winteringham, which could mean 'settlement of the followers of Winta', on the south shore of the Humber estuary, near the Roman road of Ermine Street. Naturally, even if the place name is derived from the personal name Winta, it need not be the same Winta as the one listed in the kings' genealogy. However, it may indicate a person of some authority with the right name in the right area, and is thus consistent with the genealogy.
Bede does not mention any kings of Lindsey by name. In his Ecclesiastical History he describes Paulinus, Bishop of Northumbria in 625-633, baptising the 'prefect' of the city of Lindocolina (modern Lincoln) and conducting a mass baptism in the River Trent in the presence of King Eadwine (Edwin) of Deira/Northumbria.
Paulinus also preached the word of God to the province of Lindsey, which lies immediately south of the Humber and extends to the sea. His first convert was Blaecca, Reeve of the city of Lincoln, with all his family.
The priest Deda [...] told me that one of the oldest inhabitants had described to him how he and many others had been baptised by Paulinus in the presence of King Edwin, and how the ceremony took place at noon in the River Trent...
--Bede, Ecclesiastical History, Book II Ch. 16.
This may suggest that the king of Northumbria had some political authority in Lindsey at this period, since the Northumbrian bishop was active in Lindsey. The nature of the relationship is uncertain; it may represent Northumbrian dominance over Lindsey, or a friendly relationship with the new bishop of Northumbria ministering to an allied neighbouring territory that did not (yet) have a bishop of its own.
At a slightly later period there is clear evidence of hostility and Northumbrian dominance, when the monks of Bardney in Lindsey initially refused to allow (some of) the bones of King Oswald of Northumbria to be buried there after his death in 642:
In the province of Lindsey there is a noble monastery called Beardaneu, which was greatly loved, favoured and enriched by the queen [Osthryth, daughter of Oswy of Northumbria and thus Oswald's niece] and her husband Ethelred [of Mercia]. She wished that the honoured bones of her uncle be reinterred there. But when the waggon carrying the bones arrived towards evening at the abbey, the monks were reluctant to admit it; for although they acknowledged Oswald's holiness, they were influenced by old prejudices against him even after his death, because he originally came from a different province and had ruled them as an alien king.
--Bede, Ecclesiastical History Book III Ch. 11
None of the names in the Lindsey kings' genealogy appear in other sources, so none of them can be independently dated. There may be a couple of slight clues:
If we assign Beda, Bubba and Biscop to somewhere around the middle two quarters of the seventh century, at and after Paulinus' activity in Lindsey, then the admittedly inexact method of counting generations would place their immediate predecessor Caedbaed somewhere in the early seventh century*, Winta somewhere in the early sixth century, and the last name in the list somewhere around the mid-eighth century. It should go without saying that this is highly tentative.
Caedbaed contains the common Brittonic name element Cad- or Caed-, meaning 'battle'. If the name is genuine and represents a genuine ruler of Lindsey, it may indicate Brittonic familial or political connections.
The Bardney incident tells us that Oswald held royal authority over Lindsey, or at least the monks of Bardney considered that he did and resented him for it. Yet we have a separate list of Kings of Lindsey in the Anglian Collection genealogies. How to reconcile these? Three possibilities come to mind:
If Lindsey was (temporarily?) a sub-kingdom of Northumbria, with its own kings who were subject to some degree of political control from the Northumbrian kings, this would be consistent both with Bede's mention of Northumbrian authority in Lindsey and with the presence of a genealogy for kings of Lindsey. There is no particular reason why a line of sub-kings or client kings could not have continued for several generations under foreign overlordship. Or if the genealogy is in fact a king-list, some or all of the names on it may represent a succession of client kings installed by an over-king. If Lindsey's status as a sub-kingdom was based partly or wholly on force or threat, rather than voluntary alliance, this would also be consistent with the resentment displayed by the monks of Bardney.
The hostile reaction of the monks at Bardney to King Oswald's body suggests a strong and definite dislike. This could have been a personal objection to King Oswald himself as a result of some real or perceived insult or injury. However, Bede says that the monks objected to him because he came from a different province and had ruled them as an alien king. Since the monks' hostility to Oswald was purely territorial according to Bede, it is a reasonable inference that the same attitude would have applied to any Northumbrian king ruling over them. (Caveat that Bede was a Northumbrian himself and a great admirer of King Oswald, so if Oswald had committed some injustice against Lindsey or the Bardney monastery it is possible that Bede might have chosen not to mention it). How far the opinion held by the monks of Bardney was representative of the rest of Lindsey's population is unknown.
It is worth noting that the monks of Bardney evidently felt confident that they could snub Oswald (and the wishes of Oswald's niece, Osthryth) without fear of catastrophic reprisals. This is consistent with the incident having occurred shortly after Oswald's death in 642, when Northumbrian power would have been severely weakened by his defeat. Given that Oswald had been killed in battle by the Mercian king Penda, it is possible that the monks of Bardney were siding publicly with Mercia by insulting the Mercians' defeated opponent. This could reflect straightforward pragmatism, since Mercian power would have been in the ascendancy in the Midlands region after Penda's victory over Oswald, and it is usually good politics to be in favour with the winning side. Or it may reflect a preference for the Mercian kings over the Northumbrian kings. Lindsey eventually ended up as part of the later kingdom of Mercia.
The limited evidence seems to me to be consistent with a picture of Lindsey as a client kingdom with its own line of kings but subject to Northumbrian political authority in the early to mid seventh century. If the attitude of the monks of Bardney is representative, Northumbrian political authority over Lindsey may have been obtained by force or threat, and resented in Lindsey. As usual, other interpretations are possible.
Anglian Collection genealogies, available online
Bede. Ecclesiastical History of the English People. Translated by Leo Sherley-Price, Penguin Classics, 1968, ISBN 0-14-044565-X
Winteringham (scroll south to pick up the line of Ermine Street on the map)
*In Paths of Exile I made Caedbaed of Lindsey an older contemporary of Eadwine, ruling in Lindsey in 605 AD. This is the rationale.