Abstract <p>Legitimacy is crucial for entrepreneurial ventures, enabling entrepreneurs to connect with diverse audiences and enhancing chances of business survival and growth. However, the same discourses used to establish legitimacy can also serve more nefarious purposes, such as shielding organisations from public scrutiny and concealing fraudulent practices, as evidenced by recent high-profile scandals involving figures like Bernie Madoff and Elizabeth Holmes. Yet, there is a surprising gap in research on how legitimacy-building can support the development of fraudulent entrepreneurial activities. This paper addresses this gap through an in-depth case study of Sam Bankman-Fried (SBF), the so-called “Michael Jordan” of the cryptocurrency industry, who was ultimately convicted of fraud and sentenced in the USA to 25&#xa0;years in prison. Our findings show how SBF employed three distinct types of strategic ambiguity—image, mission, and ideology—to simultaneously build legitimacy and conceal fraudulent practices, thus revealing that strategic ambiguity may play a dual role: It facilitates legitimacy-building by creating ambiguous narratives that appeal to diverse audiences, while shielding entrepreneurs from public scrutiny by distracting these audiences from behind-the-scenes fraud. This study contributes to literature on the dark side of entrepreneurship explaining how legitimacy-building strategies can help entrepreneurs hide fraudulent activities. Additionally, it offers policy implications aimed at mitigating the risk of such fraudulent endeavours in the future.</p>