He only played the Master for five minutes but what a Master he was! The Tenth Doctor, Martha and Jack met him under a different guise; Professor Yana. He wasn't the villain of old, he was a kind, gentle man trying to help humanity escape to the mythical Utopia. Aided by his alien assistant Chantho, he had no memory of the Time Lord he was, not until he opened his pocket watch and his true consciousness was returned. From then on, Yana transformed from kindly old man to cruel, callous murderer. He kills poor Chantho and turns on his former friends as he seeks revenge on the Doctor. Jacobi's performance was mesmerising and proves to be a greater Master then John Simm was across his four episodes. As enjoyable as the latter was, fans would have liked an episode or two with Jacobi in the role first. At least what the audiences got was memorable indeed. Sadly Yana was shot by a dying Chantho in the closing moments of Utopia, forcing him to regenerate into Simm's Master. The rest, as they say, is history...