Katharine Delbane

 was a Jarakbeth disguised as a human to defeat Crowley, an Aberration. She developed bland, yet very detailed, memories, of a whole yet fictitious life. She never knew of her false identity. After battling Crowley to the death, she gave Mersey her personality and went back into its subconscious, never to rise again. (PDA: Heart of TARDIS)