Milton was chubby, intelligent and a genius. That was why his school mates had bullied him. Rory Williams saved him from his bullies by helping him to hide.
Milton called his father Conrad evil. Conrad had many enemies. The sons of some of them were school mates of his son Milton.
When Milton grew older he built a time machine in memrory of the TARDIS. He travelled back in time and created giant insects who would kill anyone but his younger self. By this he wanted to take revenge from being bullied. However, the time machine was a dangerous time bomb. Everything would be wiped out if he continued to use it. With the help of the younger Milton, the Doctor stopped the creatures and deactivated the time bomb. The older Milton was killed by his own creatures. The Doctor told everyone afterwards that young Milton had saved all their lives and that he was a hero. Amy later asked the Doctor if that would change anything and turn Milton into a different person. The Doctor said that he hoped so, but that only time could tell. (AUDIO: Darkstar Academy)