Kate Stewart is the Chief Scientific Officer of the Unified Intelligence Taskforce. She also happens to be the daughter of the late, esteemed Brigadier Alistair Gordon Lethbridge-Stewart, the long-time friend and colleague of the Doctor.
When she joined UNIT, Kate dropped the ‘Lethbridge’ to avoid any hint of nepotism. Practical, disciplined and determined, she is a firm believer that science leads over a more traditional military response when the Earth is under attack. She used psychic paper to summon the Doctor when the mysterious Shakri cubes arrived in the night.
If the situation arises, Kate won’t flinch from taking painful decisions. When a Zygon invasion had reached the secret UNIT base under the Tower of London, rather than allow the collection of alien weaponry to fall into the control of the Zygons, Kate threatened to self-destruct the entire Black Archive, destroying London in the process.
She regularly finds herself in the line of fire; when the presidential plane Boat One came under attack from Cybermen in mid-air, Kate was sucked out. Fortunately her father, who had been converted into a Cyberman, was able to fly up into the sky and save her.