Sarah Jane Smith played by Elisabeth Sladen
Sarah Jane Smith was a journalist for the Metropolitan magazine, and stowed away in the TARDIS after sneaking in to a scientific establishment in the pursuit of a story.
She was on the point of leaving the Doctor when he was summoned to Gallifrey. Sarah changed her mind and wanted to stay, but the Doctor dropped her close to her own time and somewhere that was not South Croydon.
She witnessed the regeneration from Jon Pertwee to Tom Baker.