The series began with schoolteachers Ian Chesterton and Barbara Wright investigating the mystery of Susan, a student who appeared to possess scientific and historical knowledge far beyond her years. Discovering the TARDIS in a scrapyard, they were involuntarily taken by the Doctor on a journey back to the year 100,000BC, and spent two years adventuring through time and space in the TARDIS.

He distrusted his first two human companions, but over time as they shared adventures together, he grew closer to them and the TARDIS crew began to become almost a family unit. Eventually, Susan would fall in love with a human freedom fighter and leave the TARDIS behind. She was soon followed by Ian and Barbara after they helped to defeat the Doctor's deadliest enemies, the Daleks (The Chase), but the Doctor always seemed to find new companions wandering on board looking for the excitement of travel through time and space.

Eventually, the toll of years put too much of a strain on the Doctor's elderly frame. After defeating the Cybermen at the Antartic Snowcap Station (The Tenth Planet), the Doctor collapsed inside the TARDIS, and before the astonished eyes of his then-companions Ben and Polly, his cells renewed themselves for the first time, giving him a completely new physical appearance and character...