Sienna Leigh Randall, an only child born to middle class parents in London, England, can be described in many ways; boring, however, isn't one of them. From the time she was very small, she showed a great enthusiasm for life, always happy and curious about the world around her. However, as she tends to be somewhat naive at times, Sienna can get herself into odd situations, a few of which require her parents to get her out of.

Never one to really care about how she looks (which drives her mother mad sometimes), Sienna nevertheless is quite a pretty child. With dark brown hair, fair skin, and even white teeth, she has often been told by her mother that were she not going to Hogwarts, she would be going to an all-girls' boarding school, after which she would be encouraged to take up modeling. Not wanting any part of this, Sienna usually rolls her eyes and runs to her father to complain.

Although Sienna does what she is told for the most part, she does have a strong stubborn streak about her and will dig her heels in when she does not want to do something. She can be rather petulant as well, although to her credit, when someone explains to her in a clear manner why she has to do something she considers unpleasant, she will understand and end up facing up to the task and doing it without complaint.

Sienna's magic first appeared when she was seven years old. While her mother was busy baking some chocolate chip cookies, she decided to pick up her pet cat, Morgana. The instant she touched Morgana, the cat's fur turned a bright pink. Completely taken off guard, she called out to her parents; while her father was quite pleased, her mother was rather annoyed, as she didn't take very kindly to the whole business of magic and had been hoping the "wizard thing" had passed her daughter by.