The Sixth Professor

While travelling with the flame-haired pirate, Charity, the Fifth Professor found himself facing regeneration when the Nestene Consciousness staged an invasion of Australia at Adelaide. The Nestenes overwhelmed the Professor's mind, doing so much psychic damage that the Timelord risked losing his mind forever. But, before Gan's mind could be destroyed, his body died; and he regenerated. Charity fought the invading Autons to get Gan back to the TARDIS.

And when the new incarnation emerged from the Green Room, he was, of course, a different man. Whereas his predecessor had been fond of thinking, puzzling, and pondering, the new Professor was more prone to action. But, he wasn't a violent man. Rather he would reason things out in his mind, and then fly into action, implementing whatever plan his brilliant mind had worked out. And often without telling anyone in his company what he had in mind.