The only Classic Doctor Who episode in which the Doctor had no companion is 'The Deadly Assassin'
The actress Billie Piper played the companion, Rose Tyler, in the show Doctor Who. Billie piper acted in seasons 1 and 2 as the doctor's companion. She also acted in seasons 4 and the episode called The Day Of The Doctor as bad wolf.
The Seventh Doctor episode Survival had the Doctor and Ace visiting the planet of the Cheetah people.
In Doctor Who, the Doctor's current companion is Amy Pond.
As far as the tv show goes, the companion he has had the strongest attachment too emotionally was Amy Pond, however, he did fall in love with one named Rose Tyler. But the one he traveled with the most was Sarah Jones Smith, who not only was the longest companion (based on episode appearances) but she was also the only (so far) classic who companion to go on an adventure with the Doctor in the New Doctor Who. The Doctor also even gave Sarah the K-9 Unit. There has also been a spin off show called the Sarah Smith Adventures. So arguably it has always been these three names that come up when a question like this is asked.
She had a minor part in that episode long before being chosen as the 11th Doctor's companion.
Jenna-Louise Colman will be the next companion alongside Matt Smith. Her first episode will be the Christmas special 2012
The Doctor and his companion are the heroes.
At the moment The Doctor doesn't have a companion. However his last companion was Donna Noble. In the recent Easter special 'Planet of the Dead' he had a one day conpanion Lady Christina de Souza. He doesn't want to take another companion, because of how he lost Donna and Rose. Amy Pond is the Doctor's companion at the moment.
The doctor's companion in 2009 was Amy Pond. The actress's name is Karen Gillan.
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Apparantly its all up to the Doctor's companion Amy's imagination to save the universe, or so that's what I heard. I can't wait to see the finale episode 'The Big Bang' :D
Episode eight of Doctor Who season five is called 'The Hungry Earth' and is set on earth in 2015, features a scientist trying to drill into the earth's core, and the return of the classic Doctor Who monsters, the Silurians.