The Philadelphia Museum of Art is receiving what director Timothy Rub characterized as a "transformational" bequest - including a major late painting by Edward Hopper - from the estate of collector Daniel W. Dietrich II, a Chester County resident who died last year.

The gift of more than 50 artworks, as well as endowment funds, announced by the museum Thursday includes contemporary works by Cy Twombly, Philip Guston, Agnes Martin, Eva Hesse, and Paul Thek.

Several important modernist pieces, in addition to the Hopper, are contained in the bequest, including works by Charles Demuth, Marsden Hartley, and Horace Pippin, and earlier American works by Thomas Cole and Albert Pinkham Ryder.

Dietrich, a philanthropist and heir to a family conglomerate that once produced Luden's cough drops, was a longtime museum supporter and a member of its contemporary art committee.

The Hopper painting, Road and Trees, an important late work from 1962, last appeared publicly in a 2013 exhibition organized by the Whitney Museum of American Art. The painting will be available for viewing at the Art Museum in Gallery 124 beginning Friday.

The bequest also contains a striking portrait by Thomas Eakins, numerous Eakins sketches, drawings, and photographs, and works by his wife, Susan Macdowell Eakins.

Rub said the gift was transformational for the museum, particularly in the context of the comprehensive promised gift, announced in 2014, of contemporary work from collectors Keith and Katherine Sachs. The museum is mounting a show this summer of works from the Sachs collection.

With the gifts from the Sachses and Dietrich, the Art Museum has become a kind of flagship of contemporary art.

"These are great benefactions, an amazing legacy here at the museum, and one that will continue to influence our work," Rub said of the Dietrich gift. "They're really transformational because we couldn't go out and get additional Agnes Martins or the Gustons or the Twomblys, certainly. The Hopper, of course, would have always been beyond our reach to acquire by purchase. So these are things that really deepen and strengthen our collection in really significant ways."

In addition to the artworks, the museum received $10 million from Dietrich's charitable funds that will serve as an endowment supporting a wide range of curatorial initiatives in contemporary art. Dietrich gave a similar sum for a similar purpose to the University of Pennsylvania's Institute of Contemporary Art last year.

Constance H. Williams, the museum's board chair, called the Dietrich bequest comparable to the museum's most generous gifts from donors like Louise and Walter Arensberg, Albert E. Gallatin, and, more recently, the Sachses.

"Dan will be remembered as a collector of great insight and a quiet visionary whose commitment both to contemporary art and to this city's cultural institutions was exceptional," she said in a statement.

The Dietrich gift "fills some significant gaps, and it deepens our collection in really interesting ways," Rub said. "We don't have a Hopper painting, which is unbelievable and rather sad in the sense that a major artist whose graphic works are represented in depth in the collection - somehow we weren't able to secure a painting by Hopper for the collection before this point. But this fills that gap, and it does so with a really very wonderful picture, a very important one, in my view."

The Dietrich gift also deepens the museum's collections, Rub said.

"We have great, great, really interesting works by Philip Guston [1913-80] from earlier in his career," he said. "We acquired, as a gift from Guston's daughter, that amazing tondo [Bombardment] from the 1930s, and then we have some works from the '50s and '60s.

"But it may be that Guston's great legacy were the figurative works he produced in the last phase of his career. And here . . . we have two great Gustons [from 1977 and 1978], really magnificent pictures, which help us build out our holdings of Guston."

The work of Agnes Martin (1912-2004) is another example of strengthening.

"There are three pictures from 1965, three paintings, an extraordinary thing," Rub said. "And then a wonderful painting from the 1980s. So from having a small but very good collection of her work, now we have a major collection of Agnes Martin's work.

"And the same would be true of Horace Pippin," Rub said, alluding to three Dietrich collection works - The Getaway (1939), The Park Bench (1946), and an oil study for Barracks (1945).

"We have some wonderful paintings by Pippin, and we've had them for many years. Now we've doubled that number, and we have some great paintings by Pippin coming from the Dietrich collection."

Dietrich's bequest also includes funds for caring for the works and for completion of the museum's acquisition of the Paul Strand Collection of photographic work. 215-854-5594 @SPSalisbury