William MacAskill (born William David Crouch on 24 March 1987) is a Scottish philosopher and author, as well as one of the originators of the effective altruism movement. He was a Research Fellow at the Global Priorities Institute at the University of Oxford, co-founded Giving What We Can, the Centre for Effective Altruism and 80,000 Hours. MacAskill is the author of Doing Good Better (2015), What We Owe the Future (2022), and the co-author of Moral Uncertainty (2020).