The final six-episode story of Doctor Who season fourteen was "The Talons of Weng-Chiang." Although the villains initially appear to be members of a Chinese tong group operating in nineteenth-century London, in the last two episode, it is revealed that the character the Chinese assassins are worshipping as the god Weng-Chiang is actually Magnus Greel, a war criminal from fifty-first century Australia. Greel had traveled back to the nineteenth century using a time cabinet, but the temporal journey damaged his cell structure and left him in need of stolen life essences to prolong his existence.
The presence of an evil time-traveling human always struck me as a very odd feature of this story. When I found out that the villain was originally intended to be the Master (who had already been seen in decayed form earlier in the season, in "The Deadly Assassin"), things seemed to make a lot more sense. What I have not found any information about is at what stage in the script preparation the Master was removed. So when was Greel introduced to the story to replaced the Master?