Robert (The Little Drummer Boy)

Robert was a human who time travelled for thirty years.

When Robert was eight, his twin brother Christopher died of cancer just after Christmas. Robert's father left the family, and his mother committed suicide. When Robert found her dead in the kitchen, he wandered outside until he found a crashed time machine. He climbed into it and was linked to it. It asked him where he wanted to go, and he chose Christmas time as the last time he was happy. The machine took him through time to different Christmases, Robert physically aging while linked to the machine even as his mind remained that of a child, unable to disconnect from the machine due to previously-sustained damage.

On several of these journeys, Robert encountered the First Doctor, Steven Taylor and Sara Kingdom, who were unknowingly tracking the time machine's distress signal. They finally found Robert inside the machine, the machine currently resembling the eight-year-old Robert even as his original body was now in his thirties. They disconnected him from the machine, and he managed to get hold of the taranium in the Doctor's pocket. It de-aged him back to eight years old.

Using the Fast return switch, the Doctor took Robert back to the last happy Christmas, where he would take his brother's place, before his father left and his mother died, using the machine's interference in history as an opportunity to bend the rules. (PROSE: The Little Drummer Boy)