Earlier this week Mr. Daskalopoulos was sitting in the lobby of the Four Seasons Hotel in New York, having flown from his home in Athens to attend a Guggenheim board meeting and take in a few museum exhibitions.

“I’ve been collecting art since I was a teenager,” he said. “I don’t know why; I guess it’s an archetypal inner urge.” Over 20 years Mr. Daskalopoulos, 53, has amassed a collection of more than 400 works by almost 200 artists, including international names like Damien Hirst, Kiki Smith, Marina Abramovic, Robert Gober, David Hammons and John Bock. Much of the collection, however, consists of overscale work, not the kind of thing that’s easy to display at home.

As a result, “most of my collection has been in the darkness of crates,” he said. In his Athens home he lives with almost no art except a “worthless carved statuette I bought in Thailand when I was 17,” as well as a painting by Rebecca Horn that he bought in 1992, his first contemporary-artwork purchase.

Recently he has been spending time scouring Athens for a space to house his collection where the public can see it. In the meantime some of his works are on view in a four-part series of exhibitions at the Whitechapel Gallery in London.

Now he is looking forward to showing about 60 more works — by a mix of well-known artists like Mr. Barney, Louise Bourgeois and Martin Kippenberger, and newer names like Nate Lowman, Paul Chan and Wangechi Mutu — at the Guggenheim Bilbao, despite the controversy the show might cause. “The art market is a financial market and an unregulated market,” he said on Tuesday morning. “I’m sure there are questionable practices. But if I was to make a list of them, this would be at the very bottom of it, if at all. Everything here is transparent. Everyone knows this is a trustee exhibition.”