Dr Elizabeth Klein was an inhabitant of a defunct alternative timeline accidentally created when the Seventh Doctor and Ace left a piece of laser technology in the hands of the Nazis at Colditz Castle in October 1944. This led to their victory in World War II. She was the sole remnant of that timeline and a companion-in-adversity of the Seventh Doctor, later having her own timeline rewritten to the "normal" one as well.
Due to the complicated temporal nature of her existence, and the effects the Seventh Doctor's own travels had on her timeline, there were several known variations of Doctor Klein.
Klein was British-born and grew up in England during World War II. Her parents, however, were German. Because of this, Klein's peers treated her with suspicion and she received a lot of abuse. Her resulting resentment towards her fellow countrymen engendered a sympathy towards fascism which led her to favour a German victory in the war.
Such a victory did come to pass after October 1944, when a piece of anachronistic laser technology from Ace's Walkman was recovered by the Nazis at Colditz Castle. It gave the Germans an edge in the nuclear race against the United States. The Third Reich developed the atomic bomb first, turned it on the Allies and won the war, creating the timeline Klein came to know as her own. (AUDIO: Colditz)
Klein became a favourite of the Führer, Adolf Hitler, who assigned her many important duties on behalf of the Reich. In 1957, she was commissioned to investigate the outbreak of a deadly virus in Kenya. She failed to trace its source and was pulled off the mission before she could investigate further. This failure haunted her as the years went by. (AUDIO: A Thousand Tiny Wings)
In 1962, Klein was working in the physics department at the University of Cambridge. She was recruited by Major Jonas Faber to analyse alien technology for the Reich. She became romantically involved with Faber, who gave her access to a device which had been kept locked away from everyone – the TARDIS. She was told its pilot had been fatally shot by a border patrol in 1955, after which his body had been stolen. Klein could not enter the vessel until a mysterious man calling himself "Johann Schmidt" gave her the TARDIS key.
Schmidt was an alternative version of the Doctor's eighth incarnation who, claiming to be a fellow scientist, fabricated a "flight log" for the TARDIS to allow Klein to pilot the ship back to any of its recent destinations. Schmidt manipulated her into travelling back to 1944 on the pretext of retrieving the Doctor so that he could teach her to pilot the TARDIS. Faber saw through Schmidt's trickery but was too late as Klein had already decided to disobey his orders and make the trip into the past. She left her lover behind, promising to make him Führer by her efforts. (AUDIO: Klein's Story)
Unfortunately for Klein, her arrival in October 1944 alerted the Seventh Doctor to the impending alteration of history and he and Ace were able to prevent it. Klein was stranded in the proper timeline. Believing her mistake had destroyed the correct version of history, she vowed to get the TARDIS back and restore her world. (AUDIO: Colditz)
Thrown back in time
With other Nazis who fled the fall of Berlin in 1945, Klein ended up in South America. She worked with Hans De Flores and earned an additional doctorate, this one in medicine. She set out for Africa, where she hoped her timeline's events would repeat in this timeline's 1950s. This would give her another chance to learn the source of the mysterious virus. Isolated in a house with other women during the Mau Mau Uprising in British Kenya in 1953, she again met the Seventh Doctor. Despite their animosity, they worked together to solve the mystery of the virus and stop the Cheylis plot to use Earth as a testing ground for biological warfare. The Doctor, knowing Klein would continue to pose a threat to history, insisted she accompany him as a companion on his travels so he could keep an eye on her. (AUDIO: A Thousand Tiny Wings)
After Klein and the Doctor left Kenya, he asked her for the story of how she came to pilot the TARDIS to 1944. Upon hearing the details, he explained to her that the enigmatic "Johann Schmidt" had been an alternative future regeneration of himself. Klein was furious to learn her world had been lost through her manipulation by the Doctor, but pretended to accept his version so she would have a chance to turn the tables. (AUDIO: Klein's Story)
She travelled with him for a lengthy time and learned how to control the TARDIS by watching him. She found it interested when they visited a planet inhabited by the Vrill. She realised that the Vrill had specialisation after seeing the Watcher. When Klein released it was the humans that were killing the Vrill she was cast out onto the surface by Rose. She found it interesting when she realised that Jackson and Steffen were fascists, and thought that her ideas might not be so alien in the universe. Her chance to betray the Doctor came when he lost his TARDIS key while trying to help a Vrill warrior hatch from its egg. Klein recovered the key and abandoned the Doctor on the Vrill planet, fleeing in the TARDIS to restore her own timeline. (AUDIO: Survival of the Fittest)
Klein's New World
Klein tried to use the TARDIS to restore her exact timeline, but failed. She created what she described as a far better one. In this new timeline, the new Reich began in 1944. She avoided trying to bring back her lost love, Jonas Faber, because she knew she would never be able to perfectly restore the past they had lost, although she told herself that she was just waiting to get the new timeline just right. By 2044, Klein had used time travel to defeat many formidable alien threats, including the Sontarans and the Daleks. Essentially, Klein took on the Doctor's role in history in this timeline, but where the Doctor averted invasions as they happened, Klein deliberately went to the future to identify past assaults and then went back in time to either ensure that events played out as they should or alter them to maintain the Reich. Despite her official position as head of Temporal Affairs to the Reich, even those she claimed to serve were afraid of her, constantly worried that her contact with outsiders would eventually inspire her to turn on them, resulting in them insisting on her taking on ‘companions’ such as Major Richter to ensure she didn’t start rewriting their own histories to suit her goals, as well as teaching others to operate the TARDIS in the event of her death.
Though the Doctor's past had been completely rewritten, his memories of his experiences with Klein resurfaced in 2044, replacing those of his alternative self. Before this, he had arranged for an attack by Selachians from the future on Earth's moonbase to lure Klein and the TARDIS there. The Selachians used future technology to destroy the TARDIS, separating its internal and external dimensions and stranding Klein in the invasion before she could prevent it by equipping the past with knowledge from the future. When the Selachian attack was complete Klein was given to the Doctor who imprisoned and interrogated her.
The Doctor told Klein she had been tried (presumably by the Time Lords, though he did not mention them by name) and took her out of the timeline with another TARDIS specially equipped to carry out her sentence. She willingly submitted to her punishment – total obliteration from time – hoping it might restore her original timeline by preventing her from ever meeting the Doctor.
The actual outcome was quite different. The prime reality was restored and another Dr Elizabeth Klein came to be. This was a Klein known for her triumphs working for UNIT. Her personality appeared to be the same, except that this new Klein devoted her talents to the protection of Earth. Upon meeting the Doctor in the true timeline, she recognised him slightly although her experiences with him had been erased. (AUDIO: The Architects of History)
The "new" Klein
In the corrected timeline, Elizabeth Klein was the biological daughter of Nazis Kurt Schalk and Elisabeth Volkenrath, but was later adopted by Ralf and Mutte Klein. (AUDIO: Daleks Among Us) Since much of her education remained the same, she ended up becoming the scientific advisor to UNIT whilst Colonel Lafayette was the commanding officer of the British Branch. She was constantly nervous about seeing the Seventh Doctor, whom she called the Umbrella Man, as he was checking up on her, to make sure that the Nazi version of her would not reassert herself. It was on a field mission in central London where she met another version of the Doctor, who helped her stop a "power vampire". After reports from Sergeant Pete Wilson about weird goings on in one of the neighbouring buildings, she discovered mind leeches and with this other Doctor; she managed to stop them but not before Private Oscar Phillips lost his mind completely.
Another invasion occurred, this time involving the Skyheads, during which Colonel Lafayette was killed, so she had to deal with another CO, Major Wyland-Jones. Almost immediately after making peace with the Skyheads, there was an invasion attempt in Germany, where she was almost killed by the Lava Spiders. Here she met the Umbrella Doctor and Raine Creevy, escaping from a dimensional tear. She immediately mistrusted him. Due to this when to simultaneous invasions of some cubes in Nevada, USA and the Nexus in Tokyo, Japan, she went with the Umbrella Doctor to America whilst the other Doctor and Raine when to Japan.
After discovering that the other Doctor was in fact the Master, she started to trust the Umbrella Doctor. She had the knowledge to convert the Doctor's TARDIS forcefield, left behind during the Omega business, to protect Raine, Major Wyland-Jones and Sergeant Wilson from Arunzell and the Tolians. When the Doctor defeated the Master, he vowed not to spy on her again and gave her a space-time telegraph so the next time they met it was on her terms not his. (AUDIO: Dominion)
However, this turned out not to be the case, as in 1990, the Doctor asked her to come travelling with him again, although he had an ulterior motive for asking her; aware that his current incarnation was coming to an end, the Doctor wanted to deal with certain loose ends before his regeneration in case his next incarnation would lack the necessary ruthlessness to go as far as would be required to deal with those threats. Unbeknownst to them at first, Klein's assistant Will Arrowsmith, eager to meet the Doctor, stowed away aboard the TARDIS and was brought along. (AUDIO: Persuasion)
Together, the three of them worked to resolve the mystery of a device called "the persuasion machine", which was invented by Kurt Schalk, Elizabeth's biological father, a relation the Doctor suspected but was not able to confirm till much later.
The device was inspired by the manipulations of the struwwelpeter, two powerful "god-like" entities wishing to help "heal" the universe. The machine became a sought-after commodity, and led Klein, Will and the Doctor to attempt to steal it from an auction where it was to be sold. However, the auction fell apart when Sontaran forces attempted to take it over by force, and during the chaos, it was discovered that the man everyone believed to be Schalk was actually his assistant, the two having used the machine to 'program' themselves to believe they were each other and conceal its true plans. (AUDIO: Starlight Robbery)
During their travels, Elizabeth came to realise the reason the Doctor constantly checked up on her, and that her past had been heavily rewritten to allow her to exist in the "real" timeline.
Eventually, the three TARDIS travellers followed the trail to the planet Azimuth, where they finally confronted Schalk, alongside Davros, a clone of his younger self, and a squad of Daleks for control of the completed machine, where Elizabeth finally discovered the truth of her existence — she had been bred in a lab during the final years of the Second World War to be the perfect control unit for the persuasion machine. She was able to foil the plans of both Davros and his "son" by unwittingly convincing her biological mother, a cold-blooded high-ranking Nazi official, to replace her inside the Machine, which overloaded and was destroyed, killing her mother. Elizabeth, at this point, was trapped in the past, a prisoners of the Russians, having been left behind when her biological mother took the TARDIS back to Azimuth via the fast return switch, and was about to face a firing squad, just as the Doctor and Will came to rescue her, although the rescue didn't exactly go to plan. (AUDIO: Daleks Among Us)
Klein was a fervent believer in National Socialism and the benefits of fascism in general. Although she held that the needs of the many outweighed the needs of the few, she formed close, compassionate relationships with people, as evidenced by the impact Lucy's death had on her (AUDIO: A Thousand Tiny Wings) and her concern for the Vrill. (AUDIO: Survival of the Fittest) She knew of the atrocities which Nazis like Mengele committed, but differentiated their actions and ideals, saying that Mengele went too far. (AUDIO:A Thousand Tiny Wings)
Rather like Liz Shaw, Klein was recruited from university. She showed an interest in and knowledge of the more esoteric and experimental sciences, such as time travel. Faber said she was unlike many of her contemporaries, with an open, questioning, mind. Before her removal from history, she came to agree with the Doctor on some points, particularly with his observation that no matter how much she changed history, it would never feel completely "right". (AUDIO: The Architects of History)