Born Gregor Kipermann in Ukraine, Cooper was raised in Philadelphia. After graduating with a degree in Hebrew studies from Gratz College, he went on to study music at the Curtis Institute of Music and painting at the Pennsylvania Academy of Fine Arts, both in Philadelphia. In 1927 and 1928, Cooper was awarded fellowships to study in Paris with André Lhote, an influential cubist.
After returning to the US, Cooper first became a cantor in Philadelphia followed by a similar position in Baltimore. All the while, Cooper was able to paint more than 1,200 portraits including many Baltimore luminaries. Twenty-eight of his portraits are displayed at the National Jockeys Hall of Fame at Pimlico Race Course, the site of the Preakness Stakes, and eight more, all judicial or political figures, are with the Maryland State Archives. His portrait of opera star Roberta Peters hangs in the Metropolitan Opera House, and his portrait of Golda Meir is in Hadassah Hospital in Jerusalem.