The Toclafane are the humans that went to Utopia, in cute little metal cases. Thanks to the Master. Since the Doctor locked the TARDIS' coordinates to only earth 2008 or the earth three trillion or whatever, he went there and found the humans he'd sent on in that rocket, and created the Toclafane out of them.
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And they kill off the Master? WHYYY. I LOVE JOHN SIMM'S MASTER. :((((( I must go cry now.
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