The Doctor is an alien, a Time Lord from the planet Gallifrey. He travels in his space-time-ship TARDIS, with which he can go anywhere in time and space. "TARDIS" stands for Time And Relative Dimension In Space. The Doctor usually takes other people with him, who are usually called "companions" or "assistants". The Doctor and his companions travel through space and time, have a lot of adventures, and often save many people (except if they died first).
The character of the companion was there so that the people watching the series could identify and feel close to a character. The companions were often present-time humans, so people could feel close to them, and they knew as much as the viewers. Because of this, the Doctor could explain things to his companions, and at the same time to the viewers.
Number 5: Martha Jones
Martha Jones is introduced in the 2007 series of Doctor Who, first appearing in the episode "Smith and Jones". When the hospital she works at is moved to the Moon, Martha helps save the day alongside an alien time traveller known only as the Doctor (David Tennant). To thank her for her help, the Doctor invites her to join him for one trip in his time machine the TARDIS, but he later accepts her as his full-time "companion", admitting that she was "never just a passenger", and he even gives her the key to the TARDIS. Nevertheless, she becomes frustrated because the Doctor does not realise her feelings for him, When the Doctor falls in love(while believing himself to be a human) in the "Human Nature"/"The Family of Blood" two-parter, a pained Martha claims "You had to go and fall in love with a human... and it wasn't me". In the last episode of the series she spends a year travelling the world in a plan which saves the Doctor and reverses time, undoing the Master's actions.
The character reappears in the 2008 series of the Doctor Who spin-off Torchwood, which focuses on occasional Doctor Whocompanion Jack Harkness. She first appeared in the episode "Reset" as part of a three-episode story, Later in the Fourth Series of Doctor Who, Martha returns for a three-episode arc beginning with "The Sontaran Stratagem" and ending with "The Doctor's Daughter", Agyeman appears in the role again for the final two episodes of the series, "The Stolen Earth"/"Journey's End",where she has been promoted to a US division of UNIT.
Number 4: Rose Tyler
When first seen, Rose is 19 years old and working in a shop named Henrik's. She has a boyfriend named Mickey Smith, and lives in a apartment with her mother Jackie Tyler in the Powell Estate in London. Rose left school without taking her A-levels but won the bronze medal in an under-sevens gymnastics competition at her school. Her father, Pete Tyler died in 1987 in a car accident, the year after Rose was born. When she was twelve, she received a red bicycle for Christmas, which was given to her by the Doctor after meeting Rose in the future.
Ninth Doctor saves her from aliens named Autons then he destroy the building. She helps the Doctor to defeat the autons then decides to travel with him.
While they are travelling, the Doctor and Rose realise that the words "Bad Wolf" follow them around. They discover that Rose herself is the Bad Wolf, and that the words are a message. They tell Rose that she must travel to the future to absorb the energies of the time vortex, to save the Doctor and the Earth from the Daleks. By absorbing the power of the TARDIS, she destroy the Daleks, brings Captain Jack back to life and leaves the words "Bad Wolf" through the universe as clues that are seen throughout the series.
Soon the energies she absorbed begin to destroy her body. The Doctor, through a kiss, absorbs the power, sacrificing his ninth incarnation and regenerating before Rose's eyes into the Tenth Doctor.
At the beginning of season 2, Rose and the Doctor travel "farther than we've ever gone before" to New New Earth. There they meet the Face of Boe again and help defeat some cat-nurses. Over the course of season two, we learn that Rose has a crush on the Doctor, a point that is made strongly in 2.03 (when she competes for the Doctor's affections with former companion, Sarah Jane Smith) and 2.04 (when the Doctor falls for Madame de Pompadour). Toward the end of the season, the Doctor starts to return affection for Rose, ending in the finale where Rose is trapped in a parallel universe (that looks just like ours) with her mother, Jackie, Mickey, and her parallel-universe father, Peter Tyler.
Number 3: Donna Noble
During the 2006 series Christmas episode "The Runaway Bride", Donna Noble is a temporary secretary at H.C. Clements in London, a security firm which, unknown to her, hide the Torchwood Institute up until its collapse following the events of "Doomsday", and was then taken over by an alien intelligence. Her parents are Geoff and Sylvia Noble.
On Christmas Eve, the day of her wedding, she is accidentally pulled into the TARDIS because she has been drugged with Huon particles by her fiancé, Lance Bennett, because he was told to do so by Empress of the Racnoss. She aids the Doctor in defeating the Racnoss Empress, but says no to his invitation to travel with him — she is frightened not only by his adventures, but also by the Doctor himself. Having seen him commit genocide on the Racnoss, she urges him to find a new companion to act as his moral support. It was revealed later in "Turn Left" that the Doctor would have been killed while stopping the Racnoss if Donna was not there. Reappearing in April 2008's Series four premiere, "Partners in Crime", Donna has become dissatisfied with regular life and more interested in the bigger picture. She regrets declining the Doctor's offer and has been investigating unusual phenomena in the hopes of finding the Doctor for some time. When investigating Miss Foster and Adipose Industries, the Londoner and the Time Lord are finally re-united. She expresses her regret to the Doctor for not joining him and after stopping Foster's plans to convert the whole of London into Adipose children she joins him in the TARDIS as a regular companion. She makes it explicit, however, that she has no romantic attachment to him as Martha Jones and Rose Tyler did.
In "The Fires of Pompeii", Donna continually argues with the Doctor over the moral issue of whether or not he should save the inhabitants of Pompeii from the eruption of Mount Vesuvius the next day. Ultimately, they are forced to cause the eruption to happen, weighing the destruction of the city against the fate of the whole world.
Donna was the Doctor's full time companion for all 13 episodes of Series 4. Her return to the series sees her with her maternal grandfather, recurring character Wilfred Mott, as well as her mother, Sylvia. Mott is played by Bernard Cribbins, whose appearance as a newspaper seller in Voyage of the Damned was merged into his new role following the death of Howard Attfield who played Donna's father in "The Runaway Bride". Donna has encountered the Racnoss, the Adipose, the Pyroviles, the Ood, the Sontarans, The Hath, Vespiforms, the Vashta Nerada, the Judoon, the Shadow Proclamation, and the Daleks.
In the final episode of the fourth series Journey's End the Doctor erased Donna's memory of him and left her on Earth. He warned that she'd "burn up" if she remembered him.
Donna is involved in The End Of Time. At Donna's Marriage, The Doctor gives Sylvia a winning Lottery ticket before moving on to meet the first of his companions, Rose Tyler.
Number 2: Clara Oswald
Oswin Oswald is first seen in the first episode of the seventh series, "Asylum of the Daleks". She is the only survivor of the Starship Alaska. The Alaska crashed on the Asylum, a prison planet for insane Daleks. She has lived on the planet for about a year when the Doctor (Matt Smith) and his companions Amy (Karen Gillan) and Rory (Arthur Darvill) go to the Dalek Asylum to turn off the planet's force field. They are trying to do this so that an army of sane Daleks can destroy the Asylum). Clara communicates with them and helps them escape from the Daleks. She also removes all of the Daleks' memories of the Doctor. She helps the group escape and the Doctor tries to rescue her. He soon learns that she has already been captured and is now a Dalek cyborg. The Daleks had tried to keep Oswin's intellect. Because her mind could not deal with being turned into a cyborg, it created a fantasy where she survived as a human. When she learned the truth, Oswin was almost taken over by her Dalek personality, but in the end she still would not kill the Doctor. She deactivated the force field. Clara makes a final request that the Doctor remember her. She then lets the Doctor, Amy, and Rory leave the planet before it is destroyed.
Clara is introduced a second time in the 2012 Christmas special "The Snowmen". This was her first episode as the Doctor's companion. She was a young barmaid and governess in 1892. She follows the Doctor after he saves her from an attack by living snowmen. The Doctor asks her to travel with him after she enters the TARDIS, his time and space machine. Soon after this, Clara falls to her death after being attacked. Her tombstone shows her full name to be Clara Oswin Oswald. The Doctor sees that she is the same woman as Oswin from the Asylum. She even says the same things Oswin had said. Intrigued by a woman who has lived and died two times in different periods of history, he begins look across time for another Clara. The episode ends with a young woman, who could be a modern day Clara, walking through the graveyard and stopping by Clara Oswin Oswald's tomb. In a short prequel to the post-Christmas episode, the Doctor meets the modern Clara Oswald as a child, but he does not know it is her. In "The Bells of Saint John", the modern Clara meets the Doctor after being given his phone number by a woman in a shop. After an adventure in London, the Doctor asks Clara to become his companion. In "The Rings of Akhaten", the Doctor tries to learn more about who (or what) Clara really is. After watching her parents and her childhood, he finds nothing that is not normal. The episode shows that her mother died when she was a teenager. In "Hide", the Doctor goes to a haunted mansion to ask the psychic Emma Grayling about Clara. She says Clara is just an ordinary girl. "Hide" and "Journey to the Centre of the TARDIS" also show that the TARDIS does not like Clara. In a version of time which was stopped from happening, the Doctor talks with Clara about the two previous versions of her he had met. She did not know what he is talking about.
Number 1: Amy Pond
Amelia Pond is first seen in the first episode of the 2010 series, "The Eleventh Hour". She is a seven year old girl living with only her aunt, Sharon. She asks the Doctor to look at a strange crack in her wall. He is interrupted by the TARDIS. The Doctor tells Amelia that he will be back in five minutes. He does not get back for twelve years. During this time, Amelia's family and friends think The Doctor is her imaginary friend. She is treated by four psychiatrists because she keeps telling people that the "Raggedy Doctor" is real. She bites them when they tell her the Doctor is imaginary. When the Doctor returns, Amy is nineteen years old. She is working as a kissogram. Amy helps the Doctor save Earth from the Atraxi. Because of the unusual condition of the TARDIS, Amy does not see the Doctor again for two years. He asks her to travel with him. She says she will go with him, but only if he will bring her back by the next morning. She does not tell him that her wedding is the next day.
At the end of "Flesh and Stone", Amy tells the Doctor about her wedding to Rory. Because of "pre-wedding jitters", she tries to seduce him. The Doctor then finds Rory and takes him and Amy to 16th century Venice. At this point in time, Rory travelling with them. In "Amy's Choice", Amy has to deal with her feelings for the Doctor and Rory. She sees how much she loves Rory. At the end of "Cold Blood", Rory is killed and removed from history by the cracks in the universe. Amy no longer remembers him. The Doctor takes Amy to her favourite places because he feels guilty about Rory. In 19th century France, Amy forms a friendship with painter Vincent Van Gogh. Van Gogh shows a romantic interest in Amy. In "The Pandorica Opens", Rory is found in 102 AD as a Roman centurion. Amy starts to remember him.,As she remembers, it is shown that the centurion Rory is only an Auton—living plastic that looks and acts like Rory. It was made from Amy's memories to trap the Doctor. Rory tries to fight his programming but fails. He shoots and kills Amy. Amy's body is put in the Pandorica. It is a "perfect prison". It was built to keep any person trapped in it alive forever. Auton Rory guards the Pandorica while Amy is inside. She is kept inside while her body is healed. In 1996, the Pandorica is finally opened, and she is set free, by the younger Amy Pond.
The Doctor learns that Amy is connected to the cracks in the universe. He sees that they come from a temporal explosion on the date of her wedding. He talks to Amy about her house. He tells her that it is too big for only her and her aunt. Amy learns that her family had been erased by the crack in her wall. She had forgotten them. The Doctor helps her remember them. He uses the Pandorica to reset the universe and finds the sleeping Amelia on the night they met. He tells her the story of how he borrowed the TARDIS from his own people. He tells her that it is "old and new," and "big and small" and "the bluest blue that there is". He then steps into the crack in her wall to closes the cracks forever. Amy wakes up on her wedding day and is reunited with her parents. She marries Rory. At the reception, she sees that River Song's diary about time spent with the Doctor is now empty. This causes Amy to start remembering things. She says that her "Raggedy Doctor" was real and her memory of him brings him back to reality. After this, Amy and Rory choose to go with the Doctor again. They are dropped off at a "honeymoon planet" between the end of "The Big Bang" and the start of Death of the Doctor. Part of their honeymoon is on an interstellar cruise ship that the Doctor stops from crashing into a populated planet.
In the 2011 series, after an unknown amount of time, Amy and Rory return to the present. They go back to living a normal life until Amy gets an anonymous "TARDIS blue" invitation to the Utah desert. In the desert, she and Rory find the Doctor. He has aged almost 200 years since they left the TARDIS. They learn that River Song was also invited to this place. They group sees the Doctor's killed by an astronaut. They learn that the older Doctor also invited a younger version of himself. They travel with him to 1969 Washington, D.C. to investigate strange things involving the Silence. The silence is an alien race who cannot be remembered. After a person met one of the silence, they would forget everything about them as soon as they could no longer see them. While there, Amy tells the Doctor she is pregnant. She later shoots a person in an astronaut suit trying to save the future Doctor's life. She sees that the person in the suit is just a little girl. When the Doctor asks Amy later about the pregnancy, she tells him that she was wrong. The Doctor tries to learn more but learns nothing. In "Day of the Moon", Amy finds strange pictures of the astronaut girl in an old orphanage. In one of the pictures, She is holding a baby. She sees the little girl again as well as two Silence. Amy is kidnapped by the Silence. She is set free by the Doctor, Rory, and River a few days later.
During the first six episodes, Amy keeps having strange visions of a woman in an eye-patch. The woman keeps saying that "she must be dreaming". In "The Almost People" it is shown that the Amy with the Doctor is actually an avatar version. It was created with "the Flesh" brought to life by Amy's consciousness. The Doctor destroys it and he and Rory go to find the real Amy. She is, at that time, beginning to have her baby. Amy gives birth to her daughter Melody Pond. In "A Good Man Goes to War", the baby is kidnapped by the eye-patched woman, Madame Kovarian. Korvarian replaced the baby with a "Flesh" version. It is shown at the end of the episode that the name Melody Pond, when translated into an alien language is River Song. River is Amy and Rory's daughter. "Let's Kill Hitler" shows how Melody had regenerated into Mels. Mels was the childhood friend of Amy and Rory. Amy named her daughter after Mels. The episode does not show her true identity until she regenerates into River Song after being shot by Hitler. The episode also shows how Amy and Rory fell in love. In "The God Complex" the Doctor has to break Amy's faith in him. He learns that she is the reason they are brought to a prison for a being that kills by feeding on faith. The Doctor says goodbye to Rory and Amy after giving them a house and car. In "Closing Time" Amy makes a cameo appearance. It is shown that she has become a model and the face of Petrichor perfume.
In "The Wedding of River Song," Amy leads a secret organisation. Rory works for her. The Doctor and River meet again in an alternate reality after River stopped the Doctor being killed by the astronaut. Amy remembers all of her past with the Doctor but cannot remember Rory. Amy finally remembers Rory when she saves him from the Silence. She kills Madame Kovarian for taking away Melody. Reality is restored when the Doctor and River marry. Amy and Rory are back at home. They have had no contact with the Doctor since "The God Complex," but they still remember the alternate events. Later River tells Amy that the Doctor did not die in Utah and is in fact alive.