Sir Denis Mahon was one of the most distinguished art historians and collectors of the 20th century, and a determined campaigner on behalf of museums into his 90s. Mahon formed his collection over several decades, progressively demonstrating the range, significance and quality of the Italian baroque despite its comparative neglect by previous scholars. His passion and erudition – and the sheer quality of the works he brought together – changed hearts and minds and had a discernible impact on its very status in the history of European art.