The Black Sun Elder was the main ambassador of the Order of the Black Sun, sent to the planet Desrault, where trade negotiations about the uranium of the planet were ongoing with the Gallifreyans and the Sontarans. He was accompanied by a honour guard. According to Rema-Du, he was a courteous and agreeable gentleman.
In the final day of the conference, Brilox, the Sontaran ambassador, brainwashed Millenium from the Gallifreyan delegation and made her attack the Elder with her time acceleration powers. The Elder was aged to a skeleton in seconds. His death represented the start of a time war between Gallifrey and the Order of the Black Sun. (COMIC: Black Sun Rising)