Reginald Pollack (1924-2001) was a noted Human artist who lived on Earth during the 20th century.
Flint possessed one of his works among the collections he kept in his castle on Holberg 917G. (TOS: "Requiem for Methuselah")
Background
Pollack may have been one of the many aliases of Flint. Although it is equally possible that the art was just one of his many acquisitions.
Pollack, who died in 2001, is the only one of Flint's alleged historical aliases who was alive at the time that this episode was produced. All of the others were either long dead or fictional characters.