Wilfred Mott, portrayed by Bernard Cribins, is the grandfather of Donna Noble and helped the Doctor against the Master.
Unlike many of the people of Earth, Wilfred was willing to believe aliens would come in peace one day, and that humanity would eventually travel out to the stars and mingle with them. A witness to several alien invasions of Earth in 2009, he was instrumental in stopping the Time Lords’ return from within the time-lock which had sealed them in the Last Great Time War. In that effort, he trapped himself in a chamber about to be flooded with lethal radiation. His rescue was the proximate cause of the Doctor’s regeneration into his eleventh incarnation.