Jackson Lake

Jackson Lake was a Human who briefly believed himself to be an incarnation of the the Doctor.

Biography
Lake was formerly a mathematics teacher. In 1851, he moved to London with his wife and son, Frederick. They soon encountered the Cybermen. They killed his wife, and, apparently, his son. He somehow used an Infostamp to defend himself, but the device backfired, filling his mind with information the Cybermen had gathered on the Doctor. In his anguish over the loss of his family, his mind fooled itself into believing that he was actually the latest incarnation of the Doctor, newly regenerated, and amnesiac, due to the Cyberman attack.

Some time after this, he rescued a woman named Rosita from a "man made of metal." Dubbing her his companion, he began to work on his own "Tethered Aerial Release Developed In Style" or TARDIS.

Assuming the identity of the Doctor, Lake continued to act as his namesake would, investigating the "disappearance" of a man named Jackson Lake (unaware that he himself was Lake), as well as the kidnapping of many local children. His exploits soon bought him into contact with the actual Doctor. At first, the real Doctor believed Lake to be his own future incarnation, but began to suspect that the man was not who he claimed to be. After discovering enough evidence, he deduced Lake's true identity, and revealed it to him. Left aghast, Lake allowed Rosita to accompany the real Doctor as he confronted Mercy Hartigan.

The Doctor and Rosita discovered the location of the kidnapped children, as Lake struggled with the devastating truth. Having recovered his memory, but unable to remember what the Cybermen "took" from him, he found the courage to join Rosita and the Doctor, arming himself with a bandolier full of Infostamps. Using the devices to attack the Cybermen, Lake was able to fight his way under the River Thames, where the kidnapped children were used as slave labor, forced to construct the CyberKing Dreadnought, a massive weapon and Cyber-conversion factory, created for the invasion of Earth. As The Doctor and Rosita evacuated the rescued children, Lake recovered his memory completely, remembering what the Cybermen "took" from him - his son.

Finding his son in the factory, but too paralyzed with fear to save him, Lake marveled as The Doctor leaped into action and rescued the boy. He watched as the Doctor took the hot-air balloon to confront Hartigan, and end the Cyber threat. Having shared memories of the Doctor from the Infostamp, he knew that the Doctor was rarely ever thanked for his exploits, and so, he rallied the assembled masses to cheer for, and thank the Doctor.

The crisis averted, Lake and the Doctor met near the TARDIS. With Lake now a widower looking after a young son, there was no question of the Doctor inviting Lake to join him in his travels, and indeed, he was unlikely to do so anyway given his recent experience with Donna Noble. Still, Lake begged for a look inside the TARDIS, to which the Doctor gladly agreed. Overcome by the unbelievable, Lake forced himself to exit, ecstatic to have finally seen the ship. Reunited with his son, and appointing Rosita as his nanny, he then invited the Doctor to a Christmas dinner, an offer that was at first rebuked, but finally accepted. (DW: The Next Doctor)

Personality
At first, Lake was a somewhat shy, average man. Due to the effect of the Infostamp, and under the belief that he was The Doctor, Lake became a brave, dashing hero. Once his memories as Jackson Lake returned, his confidence waned, but as the threat of the Cybermen loomed, he discovered a true bravery deep within himself. The Doctor would later inform Lake that this was his own doing, not an effect of the infostamp. Even after his true identity reasserted itself, Lake retained much of the knowledge he had obtained through his brief experience as the Doctor, although he nonetheless found it hard to accept the reality of the Doctor's TARDIS.

Other information
Jackson Lake carried his own version of a sonic screwdriver which was, in fact, a real screwdriver. When asked how it was "sonic," he informed The Doctor that it does indeed make a sound, demonstrated by tapping it against a doorjamb. He also carried a fob watch. The Doctor suspected this to be a Chameleon Arch fob watch, but discovered that it wasn't. Still, the watch did contain the truth to Lake's true identity: his initials were engraved on the back.