William David MacAskill (né Crouch; born 24 March 1987)[2] is a Scottish philosopher and author, as well as one of the originators of the effective altruism movement.

[3][4][5] 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,[6] and is the author of Doing Good Better (2015)[7] and What We Owe the Future (2022),[8] and the co-author of Moral Uncertainty (2020).

[11] At the age of 15, after learning about how many people were dying as a result of AIDS, he made the decision to work towards becoming wealthy and giving away half of his money.

[12] At the age of 18, MacAskill read Peter Singer's 1972 essay "Famine, Affluence, and Morality", which motivated his philosophical and charitable interests.

He went on to be awarded a DPhil at St Anne's College, Oxford in 2014 (spending a year as a visiting student at Princeton University), supervised by John Broome and Krister Bykvist [sv].

[14] In 2009, MacAskill and fellow Oxford graduate student Toby Ord co-founded the organisation Giving What We Can to encourage people to pledge to donate 10% of their income to charities "that you sincerely believe to be among the most effective at improving the lives of others".

[24] One of the main focuses of MacAskill's research has been how one ought to make decisions under normative uncertainty; this was the topic of his DPhil thesis,[25] as well as articles in Ethics,[26] Mind[27] and The Journal of Philosophy.