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Sarah Jane Smith and Harry Sullivan from Doctor Who.
A companion is one who accompanies or assists another individual out of a sense of friendship or duty. In the Doctor Who mythos, the Gallifreyan known as the Doctor often traveled with a companion on his adventures aboard the TARDIS. In many instances, the Doctor's companions were Earth humans, and he would sometimes travel with up to three companions at any one time. The Doctor was always very close to all of his companions, and it was through him that they were able to pay witness to the great mysteries of the Universe.
On the TV series Firefly, a Companion was a job title attributed to a professional escort. While some cultures might look upon such a vocation as prostitution, it was considered a valued and respected lifestyle choice amongst the rank and file elite members of the Alliance, enabling others to share a sense of intimacy that they might not otherwise be able to enjoy with other people. The character of Inara Serra was a professional companion, which earned herself mixed feelings amongst the crew of Serenity, particularly from her former lover, Mal Reynolds. The clergyman Shepherd Derrial Book, though refraining from judgment, also felt slightly uncomfortable in her presence upon first learning about her chosen occupation.
On Earth: Final Conflict, Companion was a title given to members of the Taelon race who were assigned to various sectors or governments on Earth, such as the United Nations or even the entirety of North America. They act as liasions between Earth culture and their own and help to forge a united front against their sworn enemies, the Jaridians. In the series, Da'an was the Taelon Companion to North America, but was succeeded by his son, Zo'or.