Wolstonecroft was a human from Perfugium.
The Seventh Doctor made a deal with Death whereby the Decayed Master would have ten years of peace and sanity, at the end of which the Doctor had to kill him.
During his ten years, the Master had become a physician on the colony world with no memory of his past and took the name, John Smith. He was taken in by Wolstonecroft and inherited his house when Wolstonecroft died. (AUDIO: Master)