So, I wonder if Vortigan bears any relation to Vortigern — according to this source, Vortigern usurped the throne from Arthur’s father (Uther Pendragon)’s older brother, whom he had assassinated.
And there’s also a Vertigern/Merlin connection, detailed here. Very briefly: Vertigern was trying to build a castle, but it kept falling apart. So, he eventually turned to sorcerers for advice.
“They advised that the ground should be sprinkled with the blood of a child born to a human mother and a father from the ‘other world’.”
They found the child who fit the bill: you guessed it, Merlin. Merlin convinced Vertigern the plan with the blood sprinkling was bogus. Instead, he said the castle kept falling apart because of an underground lake with two dragons that mostly slept, but sometimes woke up, fought, and destroyed the castle in the process. Vertigern got his workers to check, and sure enough, there they were. After the red dragon beat the white one, he returned to his lair and went back to sleep, and the castle could be built.