Namesakes
Danish Kings and Queens:
1 king
King Niels 1104-1134 
Danish Prime Ministers:
1 prime minister
Niels Neergaard 1908-1909; 1920-1924
Eurovision Song Contest Winners:
1 winner
Niels "Noller" Olsen 2000 Denmark
Nobel Prize Winners:
2 medicine, 2 physics
(medicine) Niels Ryberg Finsen 1903
(physics) Niels Bohr 1922
(physics) Aage Bohr (a.k.a. Niels) 1975
(medicine) Niels Kaj Jerne 1984
Notable Musicians:
1 singer
Niels "Noller" Olsen 1954-
Notable Philosophers and Thinkers:
1 mathematician
Niels Henrik Abel 1802-1829
Notable Scientists and Inventors:
2 physicists, 1 geologist, 1 physician
Nicolas Steno (a.k.a. Niels) 1638-1686
Niels Ryberg Finsen 1860-1904
Niels Bohr 1885-1962
Aage Bohr (a.k.a. Niels) 1922-2009
Saints:
1 blessed
Blessed Nicolas Steno (a.k.a. Niels) 1638-1686