Thomas Krens, director of the foundation from 1988 to 2008, led a rapid expansion of the foundation's collections. In 1991, he broadened the foundation's holdings by acquiring the Panza Collection. Assembled by Count Giuseppe di Biumo and his wife, Giovanna, the Panza Collection includes examples of Minimalist sculptures by Carl Andre, Dan Flavin and Donald Judd, and Minimalist paintings by Robert Mangold, Brice Marden and Robert Ryman, as well as an array of Post-Minimal, Conceptual, and perceptual art by Robert Morris, Richard Serra, James Turrell, Lawrence Weiner and others, notably American examples of the 1960s and 1970s. In 1992, the Robert Mapplethorpe Foundation gifted 200 of his best photographs to the foundation. The works spanned his entire output, from his early collages, Polaroids, portraits of celebrities, self-portraits, male and female nudes, flowers and statues. It also featured mixed-media constructions and included his well-known 1998 "Self-Portrait". The acquisition initiated the foundation's photography exhibition program.