I am so surprised that no one has tried to connect him to the tree! I meant by building out his family tree....
Here he is in 1930, and his name was Isadore
"United States Census, 1930," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:X78J-6H8 : accessed 6 February 2020), Isadore Demsky in household of Harry Demsky, Amsterdam, Montgomery, New York, United States; citing enumeration district (ED) ED 14, sheet 9A, line 15, family 167, NARA microfilm publication T626 (Washington D.C.: National Archives and Records Administration, 2002), roll 1456; FHL microfilm 2,341,191.
And his marriage record has his parents. "Louisiana Parish Marriages, 1837-1957," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:QKJZ-CHV4 : 13 March 2018), Harry Demsky in entry for Kirk Douglas and Diana Dill, 02 Nov 1943; citing Orleans, Louisiana, United States, various parish courthouses, Louisiana; FHL microfilm 2,320,736.