Ian Chesterton was a science teacher in London who was curious about one of his students, Susan Foreman. Along with his fellow teacher, Barbara Wright, they decide to follow Susan back to her residence, only to find her entering a Police Box in an old junkyard. The pair meet the girls mysterious Grandfather who is unable to keep them from forcing there way into the Police Box. Upon seeing the inside of the box, the Doctor can't let them leave, and kidnaps the pair of them and takes them off on his adventures.

Ian quickly became the action hero of the quartet. Because the Doctor was a bit too old to be doing much physical work, it was often left to Ian to provide the brute force necessary. His concern, above all, is for the safety of the TARDIS crew, and in the early stories he often takes issue with the Doctor's habit of placing the group in harm's way just to satisfy his own curiosity. Most of all, however, Ian feels a great responsibility for Barbara, and will go to great lengths to protect her.

While he is doing all this protecting, we learn that Ian is a bit of a jack-of-all-trades. He manages to create fire An Unearthly Child, rides a horse, knows how to fight with swords The Romans and is knowledgeable about pressure points that can paralyze an opponent The Aztecs. His resourcefulness is a great aid to the group, and the Doctor soon appreciates Ian's presence in the TARDIS.

The Doctor does in fact become fond of Ian, and it is because of that fondness, it came as a bit of a surprise to the Doctor when Barbara and Ian decided they wanted to return home to their own time using an abandoned Dalek time machine. The Doctor is furious and tries to persuade them to stay with him by suggesting the journey might kill them, but the two teachers have made up their minds. After an emotional farewell to the Doctor and Vicki, Barbara and Ian are returned to London, albeit two years after their disappearance (presumably with much explaining to do to their friends and families). The Doctor checks on the pair of them to make sure they have arrived home safely, and candidly admits to Vicki that he will miss them.

Although, Ian and Barbara's relationship is never truly clarified in the program, in subsequent audio and literary adventures, we learn that the pair do eventually get married and have a child of their own.