Nacreus

Nacreus is a character in Doctor Who Adventures, and its upcoming spin off, Gallifrey Adventures.

Before becoming Time Lord President:
Nothing about his life prior to become the President is known as of right now.

Becoming Time Lord President:
After Rassilon sealed himself inside the crack(and later killed by The Doctor), he became the new Time Lord President. He started a new era of Gallifrey, where Time Lords aren't evil like they were in Rassilon's era.

Calling The Doctor for help:
When The Master escaped from Gallifrey, Nacreus called The Doctor for help. After The Master was defeated, Nacreus gave the Doctor a mirror, to his request.