Vortigern was a King of the Britons who is remembered for welcoming the Saxons into Britain during the dark ages and then being unable to get them to leave.

This site:  http://www.vortigernstudies.org.uk/artwho/who.htm would very much like to rehabilitate Vortigern.  He has extensive information on this site.

Our knowledge of Vortigern comes from some early sources.  Gildas, who wrote a moral history of Britain, states, around 540 BC:  “At this meeting, the council invited the Saxons in three keels from Germany, as a counter to the threat from the Picts in the north. This is followed after some time by a conflict over the annona (payment in kind), after which the Saxon federates devastate the country. Vortigern, who may have been named by Gildas, is not portrayed by Gildas as a sole ruler, or a High King if you will. He rules together with a Council, which Gildas blames equally for the disastrous policy concerning the invitation of the Saxons. Maybe looking at him as a ‘first among equals’ would be more fitting his actual position at that time. In all, Gildas’ view of the Superbus Tyrannus is almost positive; though he is judged careless and lacking foresight, he is called infaustus (unlucky), which is very mild considering Gildas’ views on the Saxons and the hindsight he had on the disaster that resulted from the Tyrannus’ policies.”    http://www.vortigernstudies.org.uk/artwho/who.htm

From Nennius, writing in the 10th century:  “The Historia Brittonum recounts many details about Vortigern and his sons. Chapters 31–49 tell how Vortigern (Guorthigirn) deals with the Saxons and Saint Germanus of Auxerre. Chapters 50–55 deal with St. Patrick ; Chapters 56 tells us about King Arthur and his battles; Chapters 57–65 mention English genealogies, mingled with English and Welsh history; Chapter 66 give important chronological calculations, mostly on Vortigern and the Adventus Saxonum.”  http://en.wikipedia.org/wiki/Vortigern

“To the old monastics, Vortigern and his Saxons were viewed as yet another scourge inflicted upon Britain.  Worse than Arianism, Pelagianism, and persecuting pagan emperors, his reign was the crowning point of the ultimate evil let loose upon the Britons, i.e. the Saxons.  These Saxons persecuted the people and devastated the church, far more thoroughly than any previous Roman Emperor!  Ironically enough, it was the veryoffensiveness of his crimes that caused the old chronologers to record and preserve records of his rise to power and the coming of his Saxon mercenaries!”  http://www.earlybritishkingdoms.com/articles/clerical.html

It’s hard to get a handle of the man beyond this.  From the other side, the Anglo-Saxon Chronicle mentions Vortigern.  It “provides dates and locations of four battles Hengest and his brother Horsa fought against the British in southeast Britain, in the historic county of Kent. Vortigern is said to have been the leader of the British in only the first battle, the opponents in the next three battles variously called ‘British’ and ‘Welsh’—which is not unusual for this part of the Chronicle. No Saxon defeat is acknowledged, but the geographical sequence of the battles suggests a Saxon retreat and the Chronicle locates the last battle, dated to 465 in Wippedsfleot, the place where the Saxons first landed, thought to be Ebbsfleet near Ramsgate. The Anglo-Saxon Chronicle presents the year 455 as the last date when Vortigern is mentioned.”  http://en.wikipedia.org/wiki/Vortigern

There is some thought that Vortigern might be mentioned on the Pillar of Eliseg, found near Dinas Bran in Wales:  “. . . the monarchy . . . Maximus . . . of Britain . . . Concenn, Pascent, Maun, Annan.† Britu son of Vortigern, whom Germanus blessed, and whom Sevira bore to him, daughter of Maximus the king, who killed the king of the Romans.”  http://en.wikipedia.org/wiki/Pillar_of_Eliseg