Originally from Wiltshire, England, Matilda (Tilly) Sparrow unexpectedly found herself working for Torchwood 5 but soon settled into her new job with enthusiasm. Her eccentricities ensuring that she fitted perfectly into her new role with ease. Tilly goes about her duties and indeed, life in general with a boundless energy and at times, an almost childlike naivety.

Being very prim and proper most of the time, she seems to exhibit strong Victorian values and is regularly surprised by many facets of everyday life. She adores pizza and remains oblivious to the fact that her colleagues continually give her alcohol in various guises, firmly believing that she is Tea Total. Tilly never goes anywhere without her umbrella and loves when she gets the chance to use explosives.

She lives in one of the TW5 accommodation rooms although she has never actually admitted this to her fellow agents, sidestepping any questions of where she lives. To her workmates, it appears that she is always first to arrive at work and last to leave.

Not much else is known about her background or private life and she tends to avoid mentioning anything relating to herself.