Sienna Tiggy Guillory is an English actress, and a former model. She is the daughter of Isaac Guillory, an Anglo-Cuban folk guitarist, and the family environment gave her an interest in the entertainment industry.

She has been featured in numerous British productions, and has gone on to roles in American productions. More recently, Guillory has appeared in a number of science-fiction and fantasy themed films aimed at teenage audiences.

Guillory, who was sixteen and still at school, began her career with a role in the television series Jilly Cooper's Riders. Following more small television and film roles, she modelled for a few years to support her acting.

She was featured in campaigns by Armani, Dolce & Gabbana, Burberry, and Paul Smith, but her biggest job was as the face of the Hugo Boss fragrance campaign from 1999 to 2002.

Afterwards, Guillory focussed her career in mostly English and BBC productions; the BBC adaptation of Take a Girl Like You was something of a breakthrough role. However, she made her name in the US television miniseries Helen of Troy (2003), in which she played the title role.

She went on to gain lead roles in films with a broader audience in the video game adaptation Resident Evil: Apocalypse (2004) as Jill Valentine and in the fantasy novel adaptation Eragon (2006) as elf princess Arya Dröttningu.