Gadra

Gadra was introduced as the Imperial Court Magician of the Eastern Empire and is the master of Razen. He has reincarnated many times so he could master magic. Every time he reincarnated, he would read the treasured books of each royal palace library and build up his knowledge.

Appearance
Gadra has the appearance of an old man with very long white hair and beard.

Personality
He has been described by Rimuru as a born egotist and that he has no relation to things like loyalty. However, he appears to value people close to him a lot, so much that avenging Adalman's death more than a thousand years ago is the sole reason that he allied himself with the Eastern Empire.

He is also an opportunist that's quick to adapt to changes. When he learned that the Clerics of the Seven Luminaries (his subject of revenge) were eliminated, and Tempest turns out to be a much greater threat than expected, he defected to Tempest without hesitation.

Background
He participated in the previous Veldora subjugation and lost his life. Before taking part in the subjugation, he performed a resurrection ritual. He defected to Tempest alongside Shinji and his team, and has been given the guest treatment since. Gadra ended up as the new guardian of the 60th floor and became a hidden boss besides the Demon Colossus.

Trivia

 * He is a Reincarnator. But rather than being a human who died in another world and reincarnated in the current one, he is a native to his world and has instead reincarnated numerous times in order to extend his lifespan using magic.