Johann Schmidt

Johann Schmidt was the eighth incarnation of the Doctor from an alternative timeline where the Nazis won World War II. In this timeline, the Seventh Doctor regenerated after he was shot in the back by Nazi soldiers in Colditz Castle in 1955. Absconding after his regeneration, he adopted the alias "Johann Schmidt" and later told Elizabeth Klein that he was a collector of sorts who had stolen the Doctor's body.

For the next ten years, he helped political prisoners escape the clutches of the Nazis and disrupted the Third Reich's "ethnic cleansing programmes." Consequently, he attracted the attention of the Nazi authorities but nevertheless maintained his liberty.

In 1965, he was able to trick Klein into setting history on its true course by programming the TARDIS to send her back to October 1944, where she met his past self and Ace in Colditz Castle. Not long after meeting Klein, the Seventh Doctor determined the true identity of Johann Schmidt though Klein herself did not become aware of it for another nine years until being reunited with the Seventh Doctor. (BFA: Colditz, BFA: Klein's Story)

''In this timeline, the Seventh Doctor regenerated for the same reason as his counterpart in the proper timeline. (DW: Doctor Who (1996))''