The General
The General was a survivor of an age-old conflict on a planet. Two species had been at war on this world for a very long time. He and Elphon were the only survivors.
The General was an old soldier, a lumpy figure on tracks, not legs made of bone like others of his kind. The Tenth Doctor's intervention at the crucial moment, when Elphon was about to take the decision to set his gun to kill and finish the war, resulted in a truce being agreed to and both parties shaking hands. This very act of contact between the last surviving male and female enabled the mix of genetic material needed for the next generation. (COMIC: The Last Soldier)