Rassilon's first regeneration

The Scrolls of Gallifrey indicated that Rassilon experienced the first regeneration on Gallifrey.

Following the Eye of Harmony's sealing, exposure to anti-matter weakened Rassilon's first incarnation. When Rassilon was confronted by Tussan and the Chancellery Guard, the stress caused Rassilon to regenerate before their eyes, and Rassilon became the first of the Time Lords. The regeneration changed Rassilon's body as the process altered its shape, with his face growing younger and his brown hair turning fair. (PROSE: The Legacy of Gallifrey ^[+]Loading...["The Legacy of Gallifrey (short story)"])

Aftermath

After a few days' rest, during which time he achieved a considerable degree of fame for his miraculous transformation, especially within the Prydonian Chapter, Rassilon assumed the leadership of the Council, declared himself President, and set about restructuring Gallifreyan society. The first thing he did was decide which Gallifreyans should be made Time Lords and which should not, arranging for about 100 men and women from each chapter to be exposed to a little of the Eye of Harmony's power, thus granting them the ability to regenerate as well, an ability that would be passed down through their children. Rassilon then set his mind to the task of conquering time travel, which would span the next few centuries. (PROSE: The Legacy of Gallifrey ^[+]Loading...["The Legacy of Gallifrey (short story)"])