In most dramatic works where the characters are based on real people, there is a point at which the character deviates from the real person. Michael Frayn works to keep this distinction as small as possible. Having studied memoirs and letters and other historical records of the two physicists, Frayn feels confident in claiming that "The actual words spoken by [the] characters are entirely their own." With that in mind, the character descriptions apply to both the representative characters as well as the physicists themselves. There is a great amount known about all of the primary characters presented in Copenhagen; the following includes those bits of information which are directly relevant and referenced in the work itself.
- Werner Heisenberg was born in 1901 in Würzburg, Germany. The son of a university professor, Heisenberg grew up in with an intense emphasis on academics, but was exposed to the destruction that World War I dealt to Germany at a rather young age. He married Elisabeth Schumacher, also the child of a professor, and they had seven children. He received his doctorate in 1923 from the physicist Arnold Sommerfeld, and went to Copenhagen to study quantum mechanics with Niels Bohr in 1924, when he was 22, and replaced Bohr's assistant, H. A. Kramers. In 1926, The University of Leipzig offered him the opportunity to become Germany's youngest full professor. Heisenberg is best known for his "Uncertainty Principle," (translated from the German Ungenauigkeit [inexactness] or Unschärfe [lack of sharpness] Relation, which was later changed to Unbestimmtheit meaning "indeterminate.") In 1927, he and Bohr presented the Copenhagen interpretation of quantum mechanics. During the Second World War, Heisenberg worked for Germany, researching atomic technology and heading their nuclear reactor program. After the war, his involvement with the Nazis earned him certain notoriety in the world of physicists, mainly due to the fact that he could have given Hitler the means to produce and use nuclear arms. He continued his research until his death in 1976 in Munich.
- Niels Bohr was born in 1885, making him 38 when Heisenberg first came to work with him. He married Margrethe Norlund in 1912 in Copenhagen and together they had six sons, two of whom died. Harry Lustig notes his biographies that "Most of the world's great theoretical physicists... spent periods of their lives at Bohr's Institute." Before the war, his research was instrumental in nuclear research, some of which led to the building of the bomb. During the war, however, Bohr was living in occupied Denmark and somewhat restricted in his research; he escaped to Sweden in 1943, just before an SS sweep which would have incriminated him through his Jewish heritage. In America, he worked in Los Alamos on the atomic bomb until the end of the war. He died in 1962 and was survived by his wife, Margrethe.
- Margrethe Bohr, known later in her life as Dronning or "Queen" Margrethe, was born in 1890 in Denmark. She was closely involved in her husband's work; he would commonly bounce ideas off of her, trying to explain them in "plain language." She died in 1984, survived by several of her children. Her son Hans wrote, "My mother was the natural and indispensable centre. Father knew how much mother meant to him and never missed an opportunity to show his gratitude and love.... Her opinions were his guidelines in daily affairs," and this relationship shows in Michael Frayn's dialogue.