Prospero was a callous and uncaring Eternal. For fun, he and others of his race descended upon an uncivilised world and bestowed the inhabitants with technology far in advance of anything they could comprehend, then retreated to the higher dimensions to watch the ensuing carnage as the primitives horrifically misused the technology and killed their world.
He arranged for a grand ball in the ruins of the wasteland where several Eternals could gather and amuse themselves by observing the few relics he had saved from the doomed world. However, the Seventh Doctor also arrived, and condemned Prospero and the other Eternals for so cruelly destroying an entire civilisation for nothing more than amusement. Presenting him with a crystallised fragment of the Time Vortex, he dropped it on the floor, summoning a time storm which swept away the Eternals and destroyed the ballroom. When the guests managed to wake up, they realised the Time Lord had destroyed their Eternal essence, sweeping them into the fold of Time and giving them a single, mortal life. Now they could learn the value of that which they destroyed with such contempt. Prospero and the other new Ephemerals were left speechless and stunned as the Time Lord left, their new bodies struggling to comprehend what had happened. (COMIC: Uninvited Guest)