Clyde Langer first appears in the second and third episodes, Revenge of the Slitheen, and is a replacement for the character Kelsey Hooper.
History[]
Like Maria, Clyde's parents are no longer living together, his father having run off with his aunt to Germany when he was young. Clyde moved to the same catchment area as Maria and Luke sometime shortly before Revenge of the Slitheen, and like them was a new student at the local school. Clyde lives with his mother, and agrees with Maria that he, like her, is happier for his parents to live apart rather than to argue. Clyde appears to put a lot of value in appearing "cool", and is a bit of a troublemaker. He initially finds Maria and Luke strange — especially Luke. However, Clyde is not without his tender side, and encourages Sarah Jane to allow Luke to call her "Mum", suspecting that this is what she really wants.
Introduced in the first episode of series one, Revenge of the Slitheen, Clyde discovered that aliens exist when he followed Maria into the school technology block and saw several Slitheen (including a child Slitheen) whom he saw change out of their disguises. While Sarah Jane was annoyed to have another person depending on her she eventually warmed to Clyde when he proved helpful in figuring out the Slitheen's weakness and in defeating the family. Clyde formed a friendship with the socially-inept-but-intellectually-brilliant Luke Smith at this time, helping him attempt to function as an average boy in social situations. In Warriors of Kudlak Luke asked Clyde to explain about girls.
In The Lost Boy, Clyde is trapped inside Mr Smith to stop him from exposing the computer as a villain and to use as a hostage. From within Mr Smith however, Clyde managed to surprise the computer by sending messages to another computer from within him.
In the Doctor Who episode "The Stolen Earth", he is said by Luke Smith to be safe in London with his mother during the Dalek invasion.
He is banned by the Judoon from extraterrestrial travel as punishment for interference in their work. Prisoner of the Judoon
During The Wedding of Sarah Jane Smith, Clyde is temporarily charged with artron energy when he comes in contact with the TARDIS while it is attempting to penetrate a time trap created by the Trickster, allowing him to briefly hurt the Trickster long enough for the Doctor to communicate with Sarah.
Alternate timelines[]
In Whatever Happened to Sarah Jane?, a mysterious being known as the Trickster changes the universe to that Sarah Jane had died as a child. Consequently, Clyde forgets about friend Maria Jackson and Luke, who temporarily cease to exist.
Clyde is mentioned for the first time in the Doctor Who episode "Turn Left". The episode sees a monster belonging to the Trickster's Brigade creating an alternate timeline where the series' hero the Doctor never meets companion Donna Noble, and is thus killed. In this new timeline, Clyde is said to have been killed along with Sarah Jane, Maria, Luke, and medical student Martha Jones while stopping the events of the Doctor Who episode "Smith and Jones".