Lady Sylvia Thaw (portrayed by Thelma Barlow) was a minor character from the Doctor Who episode "The Lazarus Experiment". A cold-hearted and greedy aristocrat, she aided Richard Lazarus in developing his Genetic Rejuvenation Device. After witnessing the device's effect on Lazarus, Thaw became enamoured by the prospect of becoming young again as well as the great wealth she could amass with the machine. She and Lazarus had also been lovers as well as business partners, but after Lazarus emerged from his machine young and strong, he admitted feeling nothing towards Thaw.
When Lazarus mutated as a result of a fault in his rejuvenation device, he attacked Sylvia and drained all of the life energy out of her, leaving her body as a skeletal husk.