The Dream Lord was a manifestation of the dark side of The Doctor, who apparently had control over dreams. He was "awoken" by specks of Psychic Pollen from the Candle Meadows of Karass Don Slava that had got stuck in the time rotor of the TARDIS console, and induced a collective dream state for the Doctor and his companions as they were warmed up. The Dream Lord drew his personality and observations from the 'dark' dimensions of the Doctor's subconscious or innermost thoughts and doubts about the course of his life and perhaps 'cavalier' treatment of others, including self-loathing, guilt, arrogance, selfishness and even lust. An additional layer to the Dream Lord's identity emerged when the Doctor described the Psychic Pollen which created the creature as a 'mind parasite,' which implies that the Dream Lord is in fact parasitic alien using the Doctor's subconscious to create a psychic form.
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He trapped the Doctor, Amy and Rory between two worlds, one in a seemingly idyllic Upper Leadworth five years in Amy and Rory's personal futures and the other in a TARDIS hurtling toward a "cold star". He told them that one was dream and one was real and that they would have to choose between them. (Actually, the Dream Lord had created both realities and they still resided in the TARDIS, which did face the danger shown in the second dream.)
Both involved deadly danger, the little village in fact inhabited by malicious aliens called the Eknodine in the guise of elderly people. Dying in the dream world would cause them to wake up in reality. The Dream Lord would appear to the Doctor and his companions in both worlds, taunting the Doctor on his insecurities and defects and pressuring Amy to assess her own priorities and 'dreams' for the future - whether she wanted a life of adventure with the Doctor or to be settled safely with Rory and a family. He seemed to relish attempting to bait the Doctor and his companions with remarks about their relationships to one another. The Doctor eventually realised that neither world was real, and managed to return them all to the waking world by destroying the TARDIS and seemingly killing himself.
Whether or not The Dream Lord had been truly defeated at the end of his debut is open for interpretation. After he had found and removed the psychic pollen, the Doctor saw the Dream Lord's face in his reflection in the TARDIS console, smiling slyly at him. Being a representation of the Doctor's inner darkness, he may never be truly defeated, but only hiding in him.(DW: Amy's Choice)
- The Dream Lord shares some similarities with a few prominent villains seen throughout the classic series, most notably the Valeyard who was also a manifestation of the Doctor's own dark side. He also shares similarities with the Celestial Toymaker, the Master of the Land, the Black Guardian (who claimed to be "evil to the Doctor's good"), and the Master (in as much as he is the Doctor's nemesis and yet defeats himself surreptitiously helping the Doctor and his companions).