Ian Chesterton is a character from the BBC
series Doctor Who
, played by William Russell. He first appears in the pilot episode, An Unearthly Child
, and leaves the series at the conclusion of The Chase
Ian was a character introducted for plot reasons. The idea being that by making him a science teacher you can provide the "educational content" that the series requires without always having The Doctor involved. This trend slacked off in later episodes though, leaving us with the other main reason for him being in the show: He was the hero figure who regularly saved The Doctor or the female characters - not that they were completely useless themselves, it just looks better on screen this way. William Hartnell was never the most agile and physically capable person and so this allowed for fight scenes without having to write in incidental characters for them all the time.
Ian was eventually returned to London with Barbara in a Dalek time machine by the Doctor. They weren't even upset that he sent them back to a point two years after they left - it could have been worse, with the Doctor controlling the time machine they could have arrived before they left, causing no end of trouble.
Ian was to return many years later in a story called Mawdryn Undead, in his capacity as a teacher at a private boy's school, but William Russell was unavailable and so the part was re-written for Nicholas Courtney's character (Brigadier Lethbridge-Stewart). According to some fans Russell appeared as Ian on the video for The Crusade, playing an elderly Ian telling the viewers about the adventure - narrating the events of the missing episode.
During the course of the series Ian got into many arguments with The Doctor, sang badly, was knighted by King Richard, spent time as a galley slave, got to see Rome burn after fighting in the arena, was nearly guillotined, met the Daleks three times, and was nearly sacrificed by the Aztecs.
I have a friend who specialises in trouble. He dives right in and usually finds a way. - Ian, The Romans