This article takes a comparative qualitative approach to explore the intertwined external accountability and legitimacy attempts of independently wealthy philanthropists. By comparing accountability forums and institutional logics stated by philanthropists, it is investigated to whom they are externally accountable and how they legitimate their controversial funding of public goods. The study compares the external accountability and legitimacy attempts of philanthropists with that of public agencies, corporations, and fundraising-dependent nonprofits. Empirically, this is a cross-sectional study of funders supporting human embryonic stem cell research in either California or Sweden. The study shows that it is through local isomorphism, rather than any specific accountability forum or institutional logic, that philanthropists are accountable and thus legitimate their giving. This is in contrast to other types of funders, which are more similar within each form when comparing accountability forums across societies, and more similar within societies in their usage of institutional logics, with certain patterned statements. In addition, philanthropists in both societies are more detached than any other type of funder as regards both specific patient populations and the general electorate. This finding raises questions on what philanthropists’ private funding for public purposes actually entails. © The Author(s) 2020.