Kirk Douglas

... was born in Amsterdam, New York, in 1916; his parents had emigrated from what is now Belarus.

Whether or not he was born Demsky is debatable. Wikipedia gives his birth name as Issur (not Issus) Danielovitch, as does his Grauniad obituary. (I'm actually writing this in March 2020, a few weeks after his death.)

According to the Grauniad, Douglas "was ... the son of Russian Jews, Herschel, a ragman who changed his name to Harry Demsky, and Bryna (nee Sanglel). The couple had only lately arrived from what is now Belarus – at the time a serious handicap to getting ahead. Yet Issur's upbringing was founded upon the preposterous gamble that ambition (and competitiveness) would bring success. That was the American way."

Wikipedia adds that Demsky was his father's brother's surname, continuing: "Douglas grew up as Izzy Demsky and legally changed his name to Kirk Douglas before entering the United States Navy during World War II."

Either way, it seems unlikely that he used both surnames (Danielovitch and Demsky) at the same time, as the question suggests.

Over to the Grauniad: "He worked his way through St Lawrence University under the name Isidore Demsky, then found employment as a professional wrestler while he took classes at the American Academy of Dramatic Arts in New York City. The wrestling was not just by necessity. Young and old, he was intensely physical, an intimidating presence (though not a big man), who always seemed capable of menace, danger and power."

"... it was under the pseudonym George Spelvin Jr that he made his Broadway debut in a production of Spring Again, in 1941. After a few more plays, he had a couple of second world war years in the US navy as a lieutenant, before being discharged on medical grounds. Thus, he was already 30 before he made his movie debut (as Kirk Douglas), playing a bespectacled and repressed weakling in The Strange Love of Martha Ivers (1946). The story goes that this break owed a good deal to his early friendship with a drama school classmate, Betty Perske, who would become Lauren Bacall."