Philippa Foot
Notes
Philippa Foot (1920–2010), English philosopher at Oxford and UCLA, one of the founders of modern virtue ethics and the inventor of the Trolley Problem, which first appears in her 1967 paper "The Problem of Abortion and the Doctrine of Double Effect". Her point was about the difference between doing and allowing harm, not about utilitarian arithmetic; the arithmetic came later.
Wikipedia: https://en.wikipedia.org/wiki/Philippa_Foot