Siân Thomas – British actress of Welsh heritage, born 20 September 1953 in Stratford-upon-Avon, Warwickshire, England. Trained at the Central School of Speech and Drama, sister of actress Sara Mair-Thomas, and long-time partner of the poet Tony Harrison (died 2025). A distinguished stage actress with credits at the Royal Shakespeare Company, National Theatre, and West End, including an Olivier Award nomination for Up for Grabs (2002) and an Off West End Award nomination for The Cherry Orchard (2017).

Her most notable film roles include Thorhild the Sarcastic in Erik the Viking (1989), Lady Darlington in Vanity Fair (2004), Madame Gaillard in Perfume: The Story of a Murderer (2006), Amelia Bones in Harry Potter and the Order of the Phoenix (2007), Edith May in War Machine (2017), and Lilly in Finding Your Feet (2018). On television she has appeared in Wide-Eyed and Legless (1993), The Worst Week of My Life (2005), The Ruby in the Smoke (2006), Midsomer Murders (2006), Merlin (2009), Atlantis (2013), New Tricks (2014), Doc Martin (2019), and Under Milk Wood (2014). She is also known for her poetry readings on BBC Radio 3 and audiobook work.