During the first half of the twentieth century a series of designers influenced and enhanced the park, including Reinhard Schuetze, S.R. DeBoer, George Kessler, Charles Robinson and the Olmstead brothers (the sons of Frederick Law Olmsted). S.R. DeBoer is recognized as the most influential, as his tenure as city landscape architect spanned almost fifty years, influencing that Park through 1960. Changes after 1960 included significant expansions by the Denver Zoo and the Denver Museum of Nature & Science (then the Natural History Museum). Both institutions have long histories in the park and contribute significantly to its character and use.