The following is a text sheet about Abnur Tharn's character traits and biography, meant for the voice actor for reference. It was shown in the official video: The Elder Scrolls Online: Elsweyr — Alfred Molina as Abnur Tharn, released May 8, 2019.
[Abnur Tharn is an] old wizard and politician, the head the Empire's Elder Council, and the [...] the Ruby Throne. The patriarch of the aristocratic Tharn dynasty, he's been managing his family's affairs for generations, maintaining and expanding their wealth and [...] has extended his life through dark magic and demonic pacts, so though he's over 150 [years old], he is strong, and vital. He speaks with natural authority, and there's no doubt that his carefully worded requests are actually commands. He's used to being the smartest man in the room, and the most ruthless.
Abnur Tharn is a master politician, relentless and persuasive, alternately cajoling and threatening. He speaks in a way that makes disagreement seem both rude and foolish. But beneath his aristocratic polish is an ever-present undercurrent of menace. He is a wily old tiger of a man, elegant, subtle, and dangerous.
In the new story, he accidentally unleashes a horde of dragons and then begrudgingly works with the Player to correct this dangerous event. He's older and showing a bit more of his age from the last time we saw him in the original main story, but still powerful and cagey, arrogant and sure of himself despite his role is causing this current situation.