Ulfcytel is first mentioned in the
Chronicle in entries for 1004, which state that Swein brought his fleet to
Norwich and destroyed the town. Ulfcytel and the councillors of the East Anglians decided that, as he had not had time to gather his army, it would be best to buy off the Danes before they did more damage. A truce was agreed, but the Danes broke it and headed from their ships to
Thetford. Ulfcytel ordered the ships to be destroyed, but those charged with the task failed to carry it out. The Danes ravaged Thetford, and on their way back to their ships they were met by Ulfcytel and a hastily assembled army. Many fell on both sides, but the Danish army got back to their ships. According to the
Chronicle, the Danes would not have escaped if the East Anglians had been able to assemble their whole army, and the Danes said that "they never met worse fighting in England than Ulfcytel dealt to them". The military historian
Richard Abels comments: "The Danes gained a
pyrrhic victory; badly mauled, they withdrew to their ships." Abels sees the ability of Ulfcytel to operate independently, without seeking the consent of the king, as an example of the viceregal powers of great local magnates under Æthelred. Although payment of tribute to the Vikings was common, it was almost always criticised when discussed in the
Chronicle. The historian
Ann Williams comments that its portrayal of Ulfcytel's decision as sensible is a notable exception which shows the ''Chronicle's'' partiality for Ulfcytel compared with other magnates who are condemned for paying tribute. A Danish Viking army led by
Thorkell the Tall spent the winter in 1009–1010 in Kent and Essex. After Easter it went to East Anglia and heard that Ulfcytel was camped with an army at Ringmere in
East Wretham, north-east of Thetford. The Danes went to East Wretham to challenge Ulfcytel's army of men of East Anglia and Cambridgeshire, and the
Battle of Ringmere was fought on 5 May. The East Anglians fled at the start of the battle, but the men of Cambridgeshire stood firm. The Anglo-Saxons suffered a heavy defeat and lost many of their leaders; the Danes then ravaged East Anglia and burnt down Thetford and Cambridge. Williams sees the invasion in 1010 as a "grudge attack", revenge for the mauling the Danes had suffered in 1004. King Æthelred died in April 1016 and was succeeded by his son
Edmund Ironside (April to November 1016), who contested the throne with Swein's son
Cnut in a series of battles over the following months. Ulfcytel is not mentioned in the
Chronicle in its account of the battles of 1016, apart from his death, but Scandinavian skaldic poems present him as one of the leaders of Anglo-Saxon forces in the last stage of English resistance, and the contemporary
Liðsmannaflokkr praises his role. The historians
Alistair Campbell and Russell Poole accept that Scandinavian descriptions of Ulfcytel's role probably have a historical basis. Poole writes: :The reference to Ulfcytel's presence at or near London in
Liðsmannaflokkr cannot be regarded as corroboration of a totally independent kind. Nevertheless, we may tentatively conclude that Ulfcytel's part in the 1015–1016 war was not confined to East Anglia, where his exact rank and power are in any case uncertain, and that like
Eirikr jarl, he played a more wide-ranging role. His contribution may have become overshadowed by Edmund's in the
Anglo-Saxon Chronicle account. The Danes besieged London in the summer of 1016, and skaldic poems describe an inconclusive battle west of London in which Ulfcytel was wounded while leading the English army. Poole comments that the difficulty with this account is that the
Chronicle states that Edmund Ironside commanded the English forces during the siege, but it is not known who took over when he left for Wessex, and it may have been Ulfcytel. Poole states that in the
Liðsmannaflokkr, "Æthelred and his son Edmund are completely ignored in favour of Ulfcytel: an awareness that from the outset he was the Vikings' staunchest and ablest opponent may be implied". Ulfcytel was one of several English leaders who were killed in the English defeat at the
Battle of Assandun on 18 October 1016. Cnut and Edmund then agreed to divide the kingdom, but Cnut became king of the whole realm following Edmund's death shortly afterwards. According to the
Supplement to Jómsvíkinga saga, preserved in the late fourteenth-century
Flateyjarbók, Thorkell the Tall killed Ulfcytel in revenge for the death of his brother. Abels comments that it is impossible to know whether this is true. ==Civilian life==