Stacy Townsend travelled with The Doctor and later, Ssard, an Ice Warrior, whom she married.
Stacy was born in 2220. (Dreadnought) Her parents were Christopher and Mary Townsend. (Placebo Effect) By 2246, she was a worker on a deep space haulage freighter, the Dreadnought, along with Bill, her fiancée. They hoped to get married at St Christopher’s Church in Norfolk. Then the Cybermen attacked. They captured Bill and subjected him to cyber-conversion. By the time The Doctor arrived in his TARDIS in response to the Dreadnought’s distress signal, he could not save Bill. However Bill was able to fight back against his conditioning enough to defeat the Cybermen. Stacy decided to join The Doctor on his travels. (Dreadnought)
The TARDIS materialised on the planet Mars in 3998, where The Doctor and Stacy found themselves caught up in Ice Warrior fighting and politics They met an Ice Warrior named Ssard who, after an adventure with The Doctor and Stacy, joined them on their travels. (Ascendance, Descendance)
Stacy and Ssard eventually left the TARDIS and decided to live in Ssard’s time period. The Doctor was invited to attend their wedding, which took place on Micawber’s World in 3999. (Placebo Effect)
Stacy and Ssard celebrated their eighteenth wedding anniversary with their three children, they were briefly wiped out of existence by the effects of the Pyramid Eternia, but after the intervention of the Twelfth Doctor and the Ancients of the Universe, the events were put back in place. (Big Bang Generation)