Bobby met the Doctor at the age of eight after being woken one night by strange noises in his closet. He opened it to discover that the TARDIS had materialised inside. He joined the Doctor for a series of adventures. They visited a planet with giant talking mushrooms (called "mooshroos" by Vicki) and ancient Rome, fought robots that looked like drills, rescued Vicki from the 'Most High' and met Conidrons and the Zaksi. He was returned to his home moments after he had left (by repeatedly pressing the fast return switch) and left the TARDIS with HiFi, given to him by Steven.
He told stories of his adventures at school and was mocked by his peers. His teachers grew worried about these stories. They contacted the Child Protective Services who decided Bobby should be separated from his widowed father and placed in a foster home. He endured years of meetings with child psychotherapists until he decided to pretend he had made it all up for attention.
About ten years later, Robert once again met the Doctor (who had not yet met Robert in his personal timeline) and accused him and his companions of ruining his life. This forced the Doctor to uphold the Web of Time and go back to take him on as a companion in the first place. (PROSE: The Schoolboy's Story)